Think the 8-foot-deep pool in your parents' backyard is the bee's knees? The Nemo 33 pool in Brussels, Belgium is 115 feet deep, son. Created for training scuba divers, it's the world's deepest by what I would guess is a pretty fair margin. If you go, remember that it's in Europe, so don't forget to pack a banana hammock.
That's really nice. It's a nice environment to teach decompression diving. I wish I could have learned in a controlled environment, Lake Erie just doesn't do it...