Umbra Rose Condos is like that, it's a safe haven for monsters living in the city.

There's a couple ways this could go.

Imagine a series of subway tunnels, connecting to various out-of-service subway stations or forgotten fallout shelters.
[img]https://i.pinimg.com/736x/7f/ca/1b/7fca1bb4e75c28c98f83b2bfefe91cbf.jpg[/img] It would work really well if you're treating this as an underground railroad for monsters.

Perhaps there's a seedy-looking cafe or bookstore that has a secret door leading to a forgotten alley, like in Harry Potter. Or an alley that leads to a cluster of forgotten buildings that have been wiped off city maps.