You don't need to do an internet search to know there are apartments for rent on Airbnb inside my friends' building in Brussels.
All you have to do is listen. Listen to the commotion at night in the building, the clomping of feet and the chatter of voices in foreign languages.
All you have to do is walk past the front door of the building at any time of day and spot the three or four tourists who will inevitably be standing there looking confused, trying to figure out how to get access to their flat, pressing all the intercom buttons and studying their phones for clues.
All you have to do is look at the piles of rubbish gathering in the common areas, which have been dumped by people who can't find the bins. Or listen out for the people drinking on their terraces late on a Tuesday night, when residents who have jobs are asleep, but those who don't are having the time of their lives.
Those people are on holiday. Obviously. And they must be a nightmare for those who aren't.
This is the downside of Airbnb and its competitors, and it's something I'd never noticed before.
Previously, I'd only ever seen good things in this system of facilitating private apartment rentals for travellers. For people like me, being able to rent a normal apartment at a reasonable price in an interesting part of a foreign city is one of the best things to happen to travel since the invention of the aeroplane.
I've been using Airbnb, and similar house-sharing websites, for a long time now and have had overwhelmingly positive experiences throughout the world. I've rented apartments in Buenos Aires, in Rome, Barcelona, Berlin and Tokyo, and they've all been great.
I've been able to stay in real homes for the price of a cheap hotel room, places with kitchens and washing machines and couches. I've stayed in parts of cities I wouldn't normally have seen, neighbourhoods devoid of the tourist crowds. I've been given an insight into the way people live – whether it's in a shoebox in Tokyo or a converted warehouse in East Berlin. I'm a huge fan.
I'm not affiliated in any way with Airbnb, and have never received any free travel or accommodation from the company. I just think that for travellers, what they do is amazing. It's a revolution.
There have been plenty of naysayers of course, most of who have a vested interest in the hotel business, warning of unregulated accommodation with no safety net for the traveller, but I've seen nothing but deserved success for Airbnb and its ilk. There's no downside.
Except, there is. And it's experienced by people like my friends in Brussels.
Because what about the residents of those tourist-free neighbourhoods that have suddenly opened up their doors? What about the normal people who find they now live in a quasi hotel that has no concierge and no check-in desk to help the bewildered masses who've begun showing up on their doorstep?
My friends' flat is a classic example. It's set close to the centre of Brussels, on a bustling street filled with cafes and bars. Their apartment building is a prime candidate for Airbnb, and sure enough, with a quick search you'll find there are three flats for rent to tourists.
In the last year or so my friends have seen a steady increase in the number of travellers arriving at their door, pressing the wrong buzzer, leaving their rubbish in the wrong place, asking for help and directions. These interactions aren't always an annoyance – to begin with they were a welcomed oddity. But the sheer number is beginning to wear them down.
This is the downside to Airbnb and its competitors. This system of house-sharing is changing neighbourhoods. It's annoying locals, creating animosity towards the people invading their once private spaces. It has taken the transient and sometimes poorly behaved tourism industry and thrown it into their homes.
There used to be a clear delineation between tourists and the people who reside in the cities they visit: locals lived in houses, travellers stayed in hotels. Now, however, the lines have been blurred, and an ever-changing cast of interlopers is arriving on doorsteps the world over.
It's not just the hotel industry that dislikes Airbnb. It's the everyday residents of tourist-heavy cities such as Rome, Paris and London. Their lives are being disrupted. Their safe-havens are no more. I can see how that would be annoying.
But the trouble is, I love Airbnb, often for the very same reasons the locals would dislike it. It's opened up a new world, and I'll probably continue to use it for as long as it's available.
I will try to put my garbage in the right places though.
Have you rented an Airbnb apartment while travelling? Share your experience by leaving a comment below.