There have been shipwrecks for as long as humans have taken to the water. According to UNESCO, 3 million sunken ships litter the ocean floor throughout the world, many of which date back thousands of years. According to UNESCO, some shipwrecks are well-documented or even planned — navies frequently scuttled ships to obstruct entries into ports or waterways. Others, on the other hand, are shrouded in mystery. Continue reading our list of shipwrecks obscured by ocean waves and by unknown causes.