Lucerne, Switzerland: The most picturesque town on Earth

In most countries, Lake Sempach would be a magnet for poets and painters, tour buses and selfie sticks. About seven-and-a-half kilometres long and three kilometres wide, it's edged by pastoral fields and tree-carpeted hills, snow-dusted peaks and cute hamlets clustered around spired churches. On a sunny day – like today – it's a spellbinding, mirror-like spectacle. Alas, Switzerland isn't like most countries. And Sempachersee (as the lake is known here) is just one of hundreds of beautiful bodies of water that sprinkle an alpine nation so naturally photogenic you'll never need to waste time twiddling with those funky Insta filters.

We breeze nonchalantly by Sempachersee as we travel by coach to Lucerne, a Swiss city set around a lake that's even larger, more iconic and gob-smacking than this one. We're on a shore excursion from Basel, one of the ports on our Jewels of the Rhine voyage with Crystal – an all-inclusive 14-night trip along one of Europe's most storied waterways, which originates, fed by glaciers, in the Swiss Alps. After arriving in Lucerne, which hugs the western banks of Lake Lucerne, my eyes drift over the sprawling, bluey-green expanse of water and towards those distant alpine mountains, which still sport a healthy coating of white powder despite the unseasonably warm spring (it's mid-May and already 28 degrees).

Tons of snow have already melted, however, and the Reuss River, which flows through the lake and re-emerges to split the city of Lucerne in half, is a gushing presence. Water churns beneath our feet as we tread the boardwalks of the Kapellbrucke (Chapel Bridge), one of several postcard-perfect sights in a city that is the sixth largest in Switzerland by population (80,000), but arguably the most aesthetically-pleasing of the lot. Distinguished by its red-tiled roof and adjoining water tower (and one-time prison and torture chamber), Chapel Bridge dates back to 1333, but has been reconstructed many times, most notably after a devastating 1993 fire – one of many blazes to have ripped through Lucerne down the centuries.

The bridge is still noticeably charred in parts, especially by its pictorial panels, which hang under the eaves and illustrate Swiss and local history. This is one of half-a-dozen or so bridges that connect the newer (but still ancient) part of Lucerne with the Aldtstadt (Old Town), a labyrinth of narrow, winding streets, thigh-straining stairways and quaint squares. With our guide, Anna Maria, leading the way, we admire dozens of charming old buildings from the late Middle Ages and Renaissance eras, when Lucerne flourished as a trading and transit post. Merchants would pitch up here after navigating Lake Lucerne with their goods loaded onto barges, some having crossed the St Gotthard Pass, a fear-inducing mountain pass that historically split southern and northern Europe.

While some Aldtstadt landmarks proved fire-resilient and still flaunt half-timbered features, most are made purely of stone and prettified by colourful paint, frescoes and polychromatic tiled roofs. We pause at Weinmarkt, a square that has witnessed many a festival and passion play, and is framed by decorative old guildhouses. Anna Maria points out a sculpture of a meat cleaver draped outside the former butchers' guild, while on the old wine market building, there's a mural of Jesus turning water into wine. We're left to our own devices for lunch, and there are oodles of enticing choices, with al fresco cafes and restaurants lining the Reuss, plus shaded spots where local workers and students picnic on baguettes, their bicycles parked at their feet.

Having over-indulged on my cruise so far (Crystal is justifiably lauded for its gourmet cuisine), I skip lunch and clamber up to the Musegg wall which, like the Chapel Bridge, was part of the 14th-century fortifications constructed to defend Lucerne. There's a remarkably well-preserved stretch punctuated with chunky watch-towers that's open to the public. Looking north as I meander along these ramparts, I glance down at playing fields and meadows that have a countryside aura with the scent of grass and manure, the trilling of birds and the sight of cattle munching and idling (there's also a mini-farm and microbrewery nearby).

Turn around and enchanting views of Lucerne and the lake await. Leaving the Musegg wall behind, I trot back down into the Aldstadt, passing souvenir shops and luxury boutiques (some bedecked with Chinese lettering thanks to all the tourists from the Far East). My group is queuing on the lakeside promenade to board MS Saphir. It's a 210-capacity "Panorama-Yacht" and a sleek modern contrast to the paddle-steamers that have traditionally serviced the lake. Seated on the canopied open-air deck as we cruise away from Lucerne, I listen to the audio guide, which unfurls intriguing local facts and folklore, interspersed with folk tunes and classical music. Johannes Brahms and Richard Wagner were among the famous figures to be seduced by Lake Lucerne as it became a fashionable destination in the 19th century.