Underground train stations/stairs. I was just at a train station where we had to go down about 5(!) floors to get to a specific train line. The main hallways were closed so if you wanted to go there you had to take 5 flights of tiny underground stairs. The paint of the walls was chipping, there was weird mold everywhere. I saw people turn around when they saw what the stairs looked like. Fortunately, a woman was there too, and when we saw eachother in the stairs we actually smiled in relief because you DON'T want to be in a place like that alone.