666 Park Avenue was apparently a book first, but this is just going to refer to the television show, which is only one season long.
Jane and her boyfriend Henry become the building managers of a luxurious residential hotel in New York City called the Drake, owned by mysterious billionaire Gavin Doran and his wife. Right away, strange things start happening, especially to Jane. She is having weird dreams, seeing things, finding secrets hidden in the basement. While supernatural events are happening to many of the tenants simultaneously, Jane is clearly the focal point, and it is revealed eventually that she has a special tie to the Drake that goes back many years. She begins to unravel its secrets with the help of companions such as a girl who lives in the building (and knows more than she seems to), and a police detective who is called to the scene.
Meanwhile, Gavin is grooming her boyfriend Henry for political office. In fact, it seems Gavin is behind a lot of the creepy things happening at the Drake. It is only clear at the very end that he is indeed Jane’s adversary in a very classic Girls Underground sense (there is sort of an intermediary adversary for a time, but he is defeated before the culmination). However, when offered a devil’s deal in the final confrontation with him, Jane takes a darker route than most Girls Underground.
This is one of those examples of the kind of GU story that takes place entirely in one building, and a very labyrinthine and magical one at that (as there are passages to other places and times within it). While not a great masterpiece, it was definitely better than expected, and had moments of true creepiness.