I am not a climber, but my boyfriend is and so I do my best to share a bit of his passion – boulder climbing.
We are lucky enough to live 10 minutes away from the first and only boulder climbing place in Paris! As it is the only one (even if you do have some others very close to the city) the place is often crowded, but it is OK because people are really nice and helpful with each other: are you stuck close to the top of your route? People will cheer you up to help you finish it!
The place consists of a kids room, a place to have a drink and eat, plus two boulder climbing rooms for everyone older than 12. The routes are changing often enough for you not to be bored and there is such a variety in it that everyone can find a level for him and then a new route to achieve!
You can buy a one-time pass and rent shoes there. Tips, try to avoid evenings, which are crowded, but lunch time on weekends is a good option.