I don't know if I'd call it a "fun" place to visit, but Butte's Berkeley Pit certainly is interesting. A former open-pit copper mine, the deep pit is now filled with almost 1000 feet of nasty toxic water. Berkeley Pit is both a Superfund site and a popular visitor attraction. These pictures will help you appreciate the size and scope of Berkeley Pit, which looms over the town of Butte, Montana. If you ever have a chance to visit in person, it's worth a stop.