There is no gate way to my building. No metal notice of keeping out those on the other side. My sister, too, lives in an apartment building building. albeit a small 6-family one--but there is a gate to cross before getting in.
I think I like the idea of a gate.
Then there are gateways to other dimensions. I think I've experienced these--where you can walk into another time-slot entirely, and it's only when you walk out and see the time that you realize you were in some kind of time warp.