Have you been to many nightclubs?  I used to go a long time ago.
It's been awhile for me also. Nightclubs use bouncers more than pubs sports bars , so I try to avoid those places. 
I wonder what the most popular Nightclub is in the world and how large it is.
I don't know. I believe the busiest nights though are usually Friday and Saturday nights.
I agree.  The weekend seems to be the time when most people go out to clubs.
I used to like when they had certain music genres for the night, like house music or hip hop
Me too.  I love listening to Hip Hop in a club.  The bass is great.
They used to also be calaled discotheque' s or disco in the 1970's and 80's,