It is considered a neutral area where "law-abiding citizens of Praetoria" can meet, drink, dance, and otherwise have fun.
The club is located in Imperial City. There is always a line to get in, but if you're a super-powered being in good standing with Emperor Cole, or if you just happen to be hot, you can get past the doorman.
You are expected to leave your coat, your cape, and your weapons with the clerk, but that's only a "suggestion" if you're in good standing with the Emperor. They won't ask if you don't tell.
The music is nothing extravagant. It's standard industrial techno music, and if you think you hear voices underneath the beats, then it's just your imagination.
The drinks are okay. The favorite is the Enriche Spritzer, which doubles the nanites in your system. If you have a troubled mind, one glass will do.
Its real draw is in who you meet there. The best of the best, the most influential in Praetoria are there. Sometimes even a Praetor or two will show up. And if you're lucky, you may even be allowed to meet them.
There is a smaller area for VIPs. This is run by Bobcat, even though she has no "official" standing with the club. She's just there, and people just accept it. If you're nice, she'll let you stay there as well. But if she doesn't like you, then she'll have her "boy toys" escort you to the service door and into the dumpster.
There is also one special place in the club that is rumored to take you to another club in another reality. If you know where this is, keep it to yourself. You really don't want the Praetors to know about it.
(See its Paragon Wiki entry for more information.)
Studio 55 was first seen in "Tales from Paragon City" #2.