If you love urban decay, then Squonk Levenque has built just the thing for you: Treptower Park, inspired by an existing abandoned amusement park in the former East Berlin. It's a dark waterly world (use the suggested Windlight settings for best effect, although personally I like Glassy for the water better than Murky) featuring not only the broken down park, but also abandoned industrial areas. (It can be hard to see these photos at this size, so click on them to zoom in.)
Click on stuff as you explore the amusement park area—you can ride the still-functioning carousel, enter the jack-in-the-box and jump on the trampoline. There's a tombstone near the landing point that will drag you underground. Peppered here and there are a few freebies, and also some helmets for sale by Squonk's partner, Miuccia Klaar, around the northeast corner.
P.S. Thanks once again to my friend M for finding cool places like this! And please do make a contribution to help support Treptower Park if you can—there's a donation thing somewhere around the middle of the sim.