What you're looking at is the Skyrim death room. (Alternate names include the Underworld, That Place With All the Dead People, and "Holy s**t, what is this?") It's a room underneath the ground that's filled with the corpses of non-player characters who have died in the game. Not all NPCs go there, of course. Only the unlucky few do. Some are allowed a proper death; others are automatically banished to this small room in the middle of nowhere where they languish in a pile in the ground for all eternity.
And while you can only reach it by hacking or running into a game bug, it's totally intentional -- the name of the room in the game's code is WIDeadBodyCleanupCell, and it's even got two little coffins down there to let you know just where you are.
Bethesda Game Studios
Hell. Nudie hell. That is where you are.
Also, although the ends of the crossed corridors are open, they don't lead anywhere. Walking out of them simply drops you back in the middle of the death room, like in those endless loop levels in Super Mario 3, but with more death stench. Even the few dead NPCs who are up walking around can't leave. The room can be useful if you accidentally killed some poor character and still need to talk to him or her (again, only a few seem to make it down there), but otherwise it's just there to make you crap your pants and never play the game again.