When architects cast an eye over man-made landmarks, they notice things others may not.
Peek into an architect's suitcase - and you'll probably discover work is never far from his or her mind. Kerstin Thompson, for example, never travels without her tape measure. "When you travel, there are always little things about the building you might enjoy that you want to measure," she says.
"If you go to some of the famous temple landscapes and pavilions in Japan, for instance, and you sit on the edge of one of their little decks looking at the garden and want to know, 'What's the height of this step and why does it feel so comfortable and so right?', then the tape measure's very handy."
William Smart is always drawing - so much so that he requests an aisle seat on planes to give his right arm room to move. "I use drawing to understand things - it's my way of understanding how things fit together," he says. "I hop on a plane and think, 'Right, now I have 12 hours or 20 hours to draw'."
When architects cast an eye over the world's man-made landmarks, they notice things that others might not: a door handle's tiniest detail or a church's perfect proportions.
"Travel reinforces to me that architecture," says Kerry Clare, "when it responds to the local traditions, materials, landscape and climate, creates unique character - which is the experience that travellers enjoy so much. If you're an architect, you're never bored when you travel."
University of New South Wales' dean of built environment Alec Tzannes first visited London's Sir John Soane's Museum (soane.org) in 1977. The famed neo-classical architect's art and antiquity-stuffed home also holds more than 30,000 architectural drawings.
Tzannes was a student, the museum's opening hours were extremely limited and "there was one grumpy old man who was the security guard".
"I asked him to open the picture gallery and he point-blank refused," Tzannes recalls. "I said, 'I've come 10,000 miles and I really want to say to you that this is a very significant work of architecture' and so on. He eventually did it, begrudgingly."
What Tzannes saw - when the gallery's hinged wall panels hung with paintings front and back were finally flipped open - was astonishing. "When you stand in front of [William] Hogarth's [eight-part series] A Rake's Progress ... and open the last panel, the spatial experience explodes because it opens up into voids and vistas and other parts of the house that you couldn't imagine were accessible from that viewing point," he says.
"It's a spectacular manipulation of space and light in a dense urban environment."
Two Parisian gallery spaces also stand out. Smart, who converted a Sydney warehouse into the White Rabbit Gallery, now one of the city's must-see art destinations, draws inspiration from the Pompidou Centre (centrepompidou.fr).
"What I love about the Pompidou Centre is watching the way people gather, their interaction with the building - it's a magnet for culture in that city," Smart says.
"I'm drawn to it more for the social aspect of that building than the architecture - although I think the architecture is fantastic."
The 1977 complex, with an external skeleton of mechanical systems and a statement escalator, houses a museum of modern art, a library and more.
It has prompted him to contemplate how architecture influences human behaviour: how a corridor can be more than a way of simply moving people around, for instance, or how a low wall can double as a seat.
Thompson contemplated lessons from Paris' Palais de Tokyo (palaisdetokyo.com) as she designed the Monash University Museum of Art. Palais de Tokyo "is a gallery with a difference - it's a very casual space and I think it's very welcoming because it doesn't have a lot of pretension around it," she says.
"It just seems to work really well as a daily neighbourhood hang-out."
Part of that looseness comes from the building's unusual history. "It had very elaborate plans drawn up for it that then got slashed," Thompson says. "The project was handed over to [French architects] Lacaton & Vassal. The building had been half-demolished by the time they got the job but, instead of worrying about what was missing, they kept everything incredibly raw."
For Camilla Block, there's inspiration in Le Corbusier's Studio-Apartment (fondationlecorbusier.fr), also in Paris. Le Corbusier, a pioneer of modern architecture, had a home studio that's "incredibly intimate and modest", she says.
"Each room is made so specifically for its purpose - Le Corbusier would have designed the whole of Rio de Janeiro given half a chance but he still understood how to make a perfect study, a perfect painting room, a perfect dining room. The bathroom is quite nutty. It's about making memorable rooms."
One of Europe's most memorable rooms is the rotunda of Rome's Pantheon. At the top of the world's largest unreinforced concrete dome is an opening - or oculus - allowing natural light to dramatically illuminate the space below.
The Pantheon's precise proportions, ancient engineering and clever lighting appeal to both Smart and Clare, whose projects include the Queensland Gallery of Modern Art.
"I just can't imagine how they got that so perfectly right," Clare says of her long-ago architectural peers.
"It's really stunning to think that 2000 years ago, they could build a dome of such size. It's not just a structural feat - they also understood light. We're spoilt these days - if you get something wrong you put a light fitting into it - but they had to get it right."
The Pantheon remains a place of worship, like two other remarkable European churches. The black-and-white striped Orvieto Cathedral (opsm.it) in Italy's Umbria appeals to Block not only for its exterior but for Luca Signorelli's interior frescos of the Last Judgment, said to have influenced Michelangelo's work in the Sistine Chapel. "Take a pen and paper because you can't take photos," she advises.
Veteran architect Philip Cox finds the French Gothic, World Heritage-listed Chartres Cathedral "awe-inspiring" for its "synthesis of art, sculpture, architecture and space", all "held together by a spidery and delicate stone structure that defies comprehension".
The remarkably preserved cathedral, with its celebrated stained-glass windows, is 80 kilometres south-west of Paris.
What makes some architecture unforgettable is the way it dovetails with surroundings.
Thompson found a prime example perched above the Portuguese coastline. The 1963 Boa Nova Tea House (ruipaula.com), north of Porto at Leca da Palmeira, is an early piece of genius from Alvaro Siza, awarded the Pritzker Prize in 1992.
For Thompson, the low-rise structure is "an exceptional building with an interior that embeds itself between rocks pounded by the Atlantic". "His buildings are always very attuned to site and amplify some aspect of it," she says.
Her advice to those making the pilgrimage is to "have a long lunch in the restaurant and finish with a drink in the bar in the late afternoon sun". "What better way to feel a space than sit and eat in it," she says.
Last month, Boa Nova reopened as a seafood restaurant with celebrity chef Rui Paula at the helm after Siza, now 81, oversaw a restoration that included reproducing the original furniture.
Landscape also underpins Stockholm's World Heritage-listed Woodland Cemetery (skogskyrkogarden.se), the final resting place of actress Greta Garbo. Gunnar Asplund and Sigurd Lewerentz began with the Nordic woodland when rethinking the concept of a cemetery.
They placed the graves - all of equal size - deep within the forest and crafted a series of chapels nestled into the surroundings.
"It's an interlocking of wild landscape and ceremonial buildings - it's kind of wild and lonely and communal and generous," says Block, who's visited in different seasons and experienced all its moods. Thompson is also a fan.
"They have beautiful details in their buildings," she says of the architects who were just 30 when they won the design competition in 1915. "For instance, the handles of the chapels have lovely little details of figures and faces and angels - they're buildings that speak to people, not just architects."
To reach another Scandinavian masterpiece - the 1939 Villa Mairea (villamairea.fi) in Finland - Clare recommends taking the scenic day ferry from Stockholm to Turku before heading 150 kilometres north to Noormarkku.
It's quite a journey but worth it, she says, to examine Aino and Alvar Aalto's 20th-century residential masterpiece that blends modern motifs with the traditional peasant architecture.
"What you notice is the connection from the indoors to the outdoors," says Clare, whose aesthetic is influenced by Scandinavian design.
"That's something we take for granted these days but in those days it was a breakthrough, especially considering the climate. It was an experimental house so it has lots of different finishes and types of spaces but it's also linked with the traditional detailing of Finnish architecture. It's quite a rich piece to visit."
Iconic homes in the United States include Frank Lloyd Wright's Frederick C Robie House (flwright.org). The 1910 Chicago house is a Prairie-style masterpiece and a forerunner of modernism.
Smart says: "It's an exquisitely proportioned building. It's famous for its ceiling heights - when you move through the house, it's got tall ceilings and low ceilings. He'd take them down very low to accentuate the drama of walking into the next room."
Clare loves West Hollywood's 1922 Schindler House (makcenter.org). "It's one of the first tilt-slab concrete houses and was built for two families," she says.
"It has this communal kitchen for two families living in different wings that open up to the landscape. It's so relevant to today - we're all talking about how to get back that idea of the extended family."
Of all of New York City's remarkable buildings, the wedge-shaped Flatiron Building with its beaux arts edifice appeals to Tzannes. "To me, it's the epitome of New York," he says.
"It was a demonstration of technology par excellence and a supremely urban building. It resonates with me to this day for the lessons it gives in making inventive, memorable architecture.
"There's a real sense of love around it and I find that hard to say about most commercial buildings."
Cox, who spends much of his time on projects in Asia, finds inspiration in India. The World Heritage-listed abandoned city of Fatehpur Sikri, 40 kilometres from Agra, home of the Taj Mahal, was briefly the Mughal empire's capital in the 16th century and features one of the country's largest mosques.
"This ruined city inspires me in its organic form, the urban spaces and the scale of buildings that respond to the arid environment," he says. "The succession of spaces delights and enthrals."
Tzannes remains enthralled with the Sydney Opera House (sydneyoperahouse.com).
"In many ways this accident, this catastrophe of the blind leading the blind, still lifts my human spirit and my sense of adventure in architecture," he says. "There's no doubt that it's a flawed gem but a gem it is. It's inspired me all my life."
View the Opera House at dawn or dusk, he says, and you'll likely see a slight shimmer or halo effect.
"That's because, cleverly, the architect has put a gloss tile to emphasise the form of the ridges and a matte tile to give you the bulk of the form," he says.
"The interplay of matte and gloss contributes to its reflective vivacity."
Practice Smart Design Studio.
Project White Rabbit Gallery, which shows contemporary Chinese art, and Promenade, a planned development on the Parramatta River.
I usually travel overseas once a year, where I'm drawn to cities. I can walk their streets for days.
My new favourite destination is Rome. It's worn-out and alive at the same time.
Travel teaches me to come back bolder in both my work and how I live my life.
I never travel without my sketchbook. I use drawing to understand things and how they fit together.
Practice Kerstin Thompson Architects.
Projects Monash University Museum of Art and sculpture forecourt, Melbourne; post-bushfire police station, Marysville, Victoria.
I usually travel to New Zealand once a month and I'll take a decent trip that's not work related once a year.
I like hotels that open up to the outside - even if that means there are hassles of noise or heat or cold. Often two or three-star hotels in somewhere like Europe are really good, because they tend to be funny, old, rattly buildings, rather than more sealed, newer buildings.
The best way to explore a city is to walk and eat. Ditch the guidebook and follow the old men: they know where the food is.
Travel teaches me to see my own home base more clearly. It can also challenge some of our conventions and expectations around living. It's always an eye-opener to travel somewhere where space is a lot more limited.
Practice Durbach Block Jaggers.
Projects Sydney Olympic Park's brickpit ring walk; the North Bondi Surf Life Saving Club.
I usually travel overseas every three years, but I try to get out of my comfort zone at least once a year.
One of the best hotels I've stayed at is the Casa Camper Boutique Hotel in Berlin. They've turned the whole idea of a hotel on its head. The rooms are designed backwards: the bathroom is at the window and the bedroom is at the back. The bedroom is very dark - it's an intimate sleep space - and the bathroom is an incredibly bright, fresh, generous space.
My new favourite destination is Copenhagen. There's an incredible gallery there called Louisiana [Museum of Modern Art], plus the Danes are doing amazing things with architecture, design and urban planning.
Practice Cox Architecture.
Projects Yulara township at Uluru, Sydney's National Maritime Museum and Melbourne's Rod Laver Arena.
I usually travel every three weeks - south-east Asia, Singapore, Malaysia, India and China. I spend half my life overseas.
I like a hotel that is central to the CBD, has good Wi-Fi connection, pool and restaurants, individual character and human scale.
My new favourite destination is Hainan in China. We are master-planning three major cities in the south of the island. It is tropical and the most southern province of China.
The best way to explore a city is by walking. The pedestrian view of the city is the best way of appreciating its urban fabric, vitality, people, spaces and landscape.
Travel teaches me to appreciate Australia better. I always come back with an eagerness to experience the Australian landscape and beaches. However, I get concerned that Australia needs to realise and better appreciate its connections to Asia.
Practice Clare Design and Professor at the University of Newcastle.
Projects Queensland Gallery of Modern Art and Melbourne's Docklands library.
We usually travel once a fortnight domestically and once or twice a year internationally - mostly we're asked to speak at conferences about environmental design. If we're invited to speak somewhere, we attach a holiday to it.
Our most enjoyable stays are in old buildings such as the paradores in Spain. They're old palaces or churches or hospitals that have been turned into hotels. They're very reasonable and you get to stay in monasteries or cathedrals - one was an old school. Because they're old buildings, they're designed with windows that open. I think air-conditioning and artificial lighting have made all these new hotels pretty awful.
My new favourite destination is Mexico. We hired a car and drove around — people said we were mad. We were stunned by the people, the culture, the colours and the climate.
I never travel without my partner Lindsay. Travel is a sharing experience for me.
Practice Dean of Built Environment, University of NSW and practising architect, Tzannes Associates.
Projects Sydney Harbour YHA, incorporating an archaeology site; public domain furniture for City of Sydney.
I usually travel overseas up to three times a year. I go to China a lot - I'm fascinated by China.
The best way to explore a city is by walking — unless it's a place like Los Angeles or Beijing. Then it's public transport or a car with a driver ideally doubling as a guide.
Travel teaches me to better understand the world and different ways of thinking. As a compulsive urban traveller, I can't help learning something every time I travel. Often we find things tantalising but they come out of a particular circumstance - it doesn't mean they're right for us. I don't like designers who just say, "This is the latest, best thing coming out of Beijing and I'm going to do it in Sydney". I think that's wrong.