The Cancun Underwater Museum
The Cancun Underwater museum is basically a series of human sculptures under the sea floor. This museum can only be visited if you are willing to dive and put on complete scuba gear or in a boat with a glass floor window. Each sculpture is created with a type of pH-neutral clay which means that marine life can grow on them. The sculptures here are now listed in the top 25 Wonders of the World by National Geographic.