Wreck diving in Oahu. We just dived at a wreck in Grand Cayman. It is a pain moving in and out of everything but it's so amazing. We were able to go into the restrooms and look at ourselves in the mirrors.
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Wreck diving in Nassau, Bahamas is great. There are lots of wreck sites littered around New Providence Island, especially along the South East coast. Check them out here: http://www.theworldswaiting.com/2011/05/get-wrecked-in-nassau.html