4. Bermuda Triangle
Also, the object of numerous investigations, studies, books and television programs, the alleged mystery of the Bermuda Triangle is one that just about everyone has heard about at one time or another. The focus of this theory is an area of the ocean that forms a crude geographic triangle between the islands of Bermuda and Puerto Rico and Miami Florida where numerous ships, boats, and aircraft have reportedly vanished without a trace. Some people believe that aliens are somehow involved, and other theories suggest there may be some natural phenomenon in the area that triggers extreme weather or unexplained events that cause various craft to be sucked into the depths of the ocean or transported to another dimension. Or something like that.