Stretched over 2 550 km and plung­ing to 10 984 m at Chal­lenger Deep, this under­sea canyon formed mil­lions of years ago when the Pacif­ic Plate dove beneath the Philip­pine Plate, cre­at­ing a 69 km-wide arc. The first sound­ing was made by HMS Chal­lenger in 1875, and the first sub­mersible descent came in 1960 aboard the Tri­este. Despite per­pet­u­al dark­ness and over 1 000 atm of pres­sure, a host of adapt­ed life thrives here, with mod­ern deep-sea ves­sels and ROVs occa­sion­al­ly explor­ing its depths.