If you've ever been to a Denny's during late night/early AM hours, you can expect to see some shenanigans because how do you end up at a Denny's at that time of day?
Drunk people, biker gangs, you name it.
But if you showed up to a Denny's in Santa Ana, California on Saturday night, you would see a giant most pit taking up the floor. A band called WACKO set up their instruments in a corner, cleared out the tables and naturally a pit opened up.
From what I can tell, the building is indeed a Denny's, but one that closed (how does a Denny's close?) and got repurposed to allow this sort of stuff to happen. So I apologize for click-baiting you.