Very cool post! I love getting glimpses of lost and almost forgotten things that are underneath the world we see in our day-to-day. The smugglers, the workers, the oppressed, the adventures, and the curious get to see these hidden relics of our past . My city has an old and abandoned series of storm-drainage tunnels that I've heard are pretty exciting, but I'd be a bit too afraid of sewer gas to go in there -- I like to be able to breathe, you know?
The flee market looks like a lot of fun -- You never know what you're going to find at those things. There's usually some real gems. Did you snag anything cool?