How to relax during Paris’s heatwave – from swimming in the Seine to visiting underground catacombs

You could grill a Croque Madame on a Parisian street this summer – or at least the fried egg that tops it. France’s capital, like so much of the country, is already on its third heatwave this year. That might make you think twice about visiting, but I’ve got a soft spot for Paris in the summer holidays. Rather than postponing a trip to Paris when a heatwave is forecast, I’ve learnt to embrace it.

I find myself going against the herd on the last day of the summer term. All Parisians who can will evacuate the city in summer, and, going the wrong way, I feel like Simba in a buffalo stampede of families with far too much luggage. Anyone who thinks France’s birth rate is falling should take the Metro at rush hour at the start of the summer holidays.

In 2024, Anne Hidalgo, mayor during Paris’s Olympic Games, dove into the River Seine and declared it safe for swimming for the first time in a century. I vividly remember the reactions of French friends. They were all along the lines of “you’d catch something nasty jumping in that” and “get ready to see Parisians with green, radioactive limbs”, punctuated by plenty of “ooh las” of disbelief.

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Fast forward two years, and my friend and I wallow in the cool waters of the Seine just opposite Île Saint-Louis. This swim spot, Bras-Marie, is hemmed in by floating pontoons, and from the water I can see towering hôtels particuliers (historic mansions) and the carved stone wreaths on the sides of Pont Louis-Philippe. Notre-Dame Cathedral sits just 600 metres away. When I was younger, I went to Friday evening “wave raves” at my local swimming pool, and the wash from passing boats here creates a similar effect to the wave machine.

Throughout July and August, as part of the annual summer event Paris Plages, there are five “wild” swimming spots in central Paris. They’re all free, and – with the exception of the swimming area at Quai de Jemmapes, which is only open on Sunday afternoons – open daily. The water quality is checked daily too, and if it’s not deemed clean enough, the swim area won’t open.

An interactive online map, Paris en Seine, is updated with green and red flags – something we discover to our detriment after walking 90 minutes along the Seine for a second swim at Quai de Grenelle, just after the Eiffel Tower, only to find that it was closed that day. Fortunately, it feels much cooler down on the footpath by the river than in the rest of the city, and Paris Plages has turned much of the riverbank into a playground and water park rolled into one. There are climbing walls, table football and giant sprinklers (all free too), and by the former Olympic village at La Villette, pedalos, kayaking and stand up paddleboards. Elsewhere, many people use the riverside weeping willows for shade as they read or sketch.

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In normal times and temperatures, Paris is frenetic. When it’s hot, the city slows to an amble. We condense the area that we explore, favouring journeys on foot rather than by metro. There are currently only six metro lines with air conditioning (1, 2, 5, 9, 11 and 14), and although they’re marginally more tolerable, I find myself sweating from places I never knew had sweat glands, like my knees.

Happily, many of Paris’s museums do have air conditioning, including the Louvre, Musée de l’Orangerie and Musée Carnavalet, all of which are on the supposedly-air-conditioned-yet-still-knee-sweat-inducing metro line 1. In short, a heatwave is the perfect time to stare at the Vitamin D-deprived face of the Mona Lisa. Cooler still, though, are the museums quite literally underground. The catacombs are 20 metres below ground level, which keeps the temperature at around 14C year-round, and although the majority of the Musée des Égouts (Museum of Sewers) is just 3 metres underground, the temperatures hover around 15-20C. There’s something rather dystopian about retreating into underground tunnels as up above the city becomes the perfect temperature for Saharan ants.

Back in 2024, when swimming in the Seine might still have turned my pale, freckled legs green and radioactive, I made the grave error of booking an Airbnb with no AC when I came to watch the Olympics. My visit coincided with a heatwave. Now, anywhere that I stay in Paris should have AC so strong that I feel as though I’ve stepped into a chest freezer, and preferably a pool as well.

This time, I stay at La Fondation in the 17th arrondissement. Not only does it have a 25m swimming pool in the basement, but it’s also a 10-minute walk from Parc Monceau. Parisian parks aren’t all created equal: Les Tuileries, with its skinny trees and distinct lack of grass, is horrible in a heatwave. The weeping willows of Parc Monceau or fat oak trees of Bois de Boulogne are far more effective natural parasols.

After that first stampede at the start of the school holidays, the city visibly empties. There’s no queueing for the free swim spots, and I wander into shaded wine bar terraces without a reservation. Planned right, I’d take a sizzling Paris over a crowded one.

Anna stayed as a guest of La Fondation.

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