Neptune Memorial Reef
aka Atlantis Memorial Reef or Atlantis Reef

The Neptune Memorial Reef is an underwater mausoleum for cremated remains and the world's largest man-made reef (covering over 600,000 square feet of ocean floor). The area was chosen approximately 3.25 miles off the coast of Key Biscayne, Florida. It is a type of burial at sea and the first phase is estimated to be able to accommodate 850 remains, with an eventual goal of more than 125,000 remains.

The man-made reef opened in 2007 after a number of difficulties, including permits. An incredible amount of planning and execution went into what was initially supposed to be a “replica” of Lost City of Atlantis, but the project shifted towards a more profitable goal by becoming the world’s first underwater cemetery and memorial park that still resembles an underwater city covering 16 acres of ocean floor. Instead of spreading ashes over ocean waters, at the Neptune Memorial Reef the ashes of loved ones are mixed with cement designed for underwater use and fitted into a mold, which a diver then places and secures into the reef. A copper and bronze plaque is then installed with the person’s name, date of birth and death with some space for an epithet. The reef stretches across the ocean floor and is designed as both a home for sea life and "a destination for divers" at a maximum depth of only 45 feet.

http://www.neptunesociety.com/memorial-reef