This is a spring-to-autumn plan (roughly April to October): Fontainebleau's sandstone climbs best in dry, cool, settled weather, and the single most important rule of the forest is that you never climb on wet or damp rock, because saturated sandstone is fragile, dangerous and easily broken. From CDG, the RER B train reaches central Paris (Gare du Nord) in about 30 to 35 minutes, cheaper and usually quicker than a taxi in traffic. If you would rather skip the plane, the Eurostar from London St Pancras arrives right into Gare du Nord in around two and a half hours. Book flights →

Base yourself somewhere with an easy Metro or RER connection; a spot near Gare de Lyon is worth considering, as that is where Saturday's train to Fontainebleau leaves from, but anywhere central works given how compact Paris is. Leave your climbing shoes packed and travel light for the city days. Search hotels →

Ride Metro line 12 to Abbesses and climb up through Montmartre, the old artists' quarter of steep lanes, vineyards and cafe terraces, to the white domes of the Sacre-Coeur basilica, which crowns the highest point in the city and looks out over the whole of Paris for free. A local guide turns the tangle of streets into a story and points you at the corners the coach crowds miss; if the steps look daunting there is a funicular up the hill. Search Montmartre walking tour in Paris on GetYourGuide →

The lanes around Abbesses and the Rue des Martyrs are full of small bistros and wine bars that fill up early with locals; wander until something feels right rather than booking a view. Keep it relaxed and turn in at a reasonable hour, because tomorrow is the big day and an early start beats the crowds in the forest.