Hardly anyone ever goes inside those buildings on the bottom. The top middle one is the entrance to the salt mines. The middle left is the exit from the salt mines. The middle right is probably related to a Nappy quest.
But I rarely see anyone inside the two bottom buildings. Most of the time, people hang around outside. Maybe if the lobby is packed full of players, you might see some side fights in there.
Top left is the entrance to the salt mines; the top right is, I think, related to a Nappyrat quest.
Edited because: Image was updated and merged, thus requiring an update to my comment.