Dutch Springs in Bethlehem, PA. It's a former limestone quarry-turned-freshwater lake, and the owners have sunk several "wrecks" (boats, a firetruck, a trolley, a tanker truck, a jet plane, and a school bus, among others) to turn the lake into a diver training ground. It's a fun place to dive, but early in the year it can be quite chilly. I was doing my drysuit training checkout dives this past weekend, and fortunately I didn't bring home a case of hypothermia!