Cat N.
Yelp
Ah, this is going to become my new neighborhood bad habit. It's perfectly situated between Odeon and St Michel - and don't balk at coming to the 6th, the tourists stay on the other side, in the Latin Quarter's gyro and fake fondue alleys! I knew I had to come here when I saw the sign that said "50s/60s/70s" music.
I'm not sure if the drink menu downstairs is different from upstairs, but since it was early-ish in the week and we weren't planning on dancing, we stayed upstairs because our bartender was so generous and fun to talk to. He made each of us custom drinks after listening to what we liked, and they were truly creative (and potent). It's fascinating to watch him make any drink, really, because he puts so much care into it. He served a bunch that he said would be on future menus, so I know I'll have to come back. They also have a unique selection of rare scotches at fair prices.
The atmosphere is more relaxed and fun here, with cocktails just as good (if not better) than the nearby Prescription Cocktail Club. Not to slander Prescription... it's another favorite of mine, but that's the sort of place I would recommend for a date, Castor Club for a good time with a group of friends.