Kristian von Homsleth is a Danish artist who aims to sink a giant, metal, star-shaped sculpture – that will have at its center a cylinder filled with (donated) human blood and hair – in the Marianas Trench toward the end of this year. Hornsleth – who considers the sculpture to be a meditation on life, eternity, and the imperviousness of large-scale art projects – expects the sculpture will remain sunk for 10 to 15 thousand years.

It got us wondering what else has been purposely sunk in the sea...

Like more sculptures! Jason de Caires Taylor – British/Guyanese artist, diving instructor, and underwater naturalist – made an underwater sculpture park in Grenada in 2006. The park is in snorkelable or divable water. The sculptures themselves are made of concrete and other materials. They are mostly human figures—we are especially fond of The Lost Correspondent, showing a solitary writer sitting at a typewriter—and as the sculptures have aged they've become covered in corals and are now mixed in with the area's abundant sea life. Taylor is now working on a bigger version of the sculpture park off the coast of Cancun.

Less pleasantly, land mines have been dropped into water to destroy ships and subs. "Naval mines," as these weapons are called, are said to have first been described in a 14th century Chinese military treatise. They've stuck around. According to a 1998 U.S. military report, "at least 30 countries are actively engaged in the development and manufacture of sophisticated new mines. Of these, 20 are known mine exporters. An even greater number of nations possess the ability to lay land mines. Although most of the world's stockpiled mines are relatively old, they remain lethal and easily upgraded." Feeling alarmed? Me, too. Luckily—unless you're a dolphin—the U.S. has trained dolphins to clear mines.

Military gear has been dropped in the water for benign purposes as well. A stash of armored military vehicles has been sunk off the coast of South Carolina as artificial reeds, to provide fish habitat (which in turn, provides fishermen and women with an easier catch). As natural reefs continue to decline, other foreign entities have also been used as artificial reefs: subway cars, decommissioned ships, garbage trucks, even human remains. These reefs have not always worked out as intended—and we're not talking about the reefs made of human remains here. In 1972, hundreds of thousands of used tires were dropped in the ocean off the coast of Ft. Lauderdale to be used as an artificial reef. Instead of providing shelter to sea life, the tires have harmed an area of the ocean floor equivalent to 31 football fields. The tires are being removed from the ocean by Army and Navy diving crews—73,000 have been taken out so far, though the operation is now suspended while the military pursues other priorities.

Other tires dropped in the ocean have a bigger value. A 1925 Brescia Type-22 Roadster was pulled from a Swiss lake after having been dumped – it's said – in 1936. The roadster was possibly dumped by a Swiss customs official after the car's French owner failed to pay taxes on the car; another version of the story has Polish architect Marco Schmuklerski buying the car and then trying to hide it in the lake, eventually losing it to the waters. The car was pulled up from Lake Maggiore in July 2009—with its tires still holding air—and sold at auction in 2010 for an astonishing $367,741.

Having nothing at all to do with vehicles is a submerged temple in Thailand. Wat Tilokaram is thought to have been built more than 500 years ago. It was high and dry for most of that time. Then, some seventy years ago, the temple went underwater when a large freshwater lake was created up and around the temple, which these days can be seen poking out of the water and can be visited by boat. Plans to restore the temple by draining the lake – home to aquatic plants and many species of fish – were bandied about, but recently abandoned on the grounds that draining the lake would hurt the temple after all these years under water, and would also hurt local fisherman. In this case, the mountain came to Mohammad, but reportedly more temples in Thailand are now unintentionally going under as sea levels rise.