Never Ending Halls

I don't know what's happening to me. Am I going insane? I walked through a door on the side of a subway tunnel, and now I'm here. I tried going back through the door but, when I turned around there was no door. Just halls that seemed to stretch on forever, with an atmosphere so dark it seemed even the light couldn't cut through it. I don't even have a recollection of how long it's been since I got here. For all I know it could be minutes, hours, days, or even weeks, as time seems irrelevant. The farther I go in, the more things start to... change. Objects like paintings don't seem so... how do I say this? Normal, anymore. I noticed the key is to keep moving, otherwise, things start to get even stranger...