Supersonic was the first club that I visited in Paris and there are so many reasons as to why I cherish it so much. Many clubs in Paris open late (compared to America, my home country) and have hefty cover charges. Supersonic was open at a reasonable time and it was free to get in! The venue looks sketchy from the outside, but the bouncers are kind and inside, the place is really comfortable and nice. They had a band playing live music, two floors to look at what's going on, and a really cool bar. Their happy hours were kind of weird (during happy hours, their beers are priced really well, but it ended pretty early) and the club closed comparatively early.
I'd recommend this place as a chill vibe/pre-game to get to see the city in a relaxing and introspective way.