Dark Ocean

Dark Ocean is an empty other dimension connected to the Digital World and it is yet inhabtited by Scubamon and Dragomon. This strange and shadowy world which is an alternate version of the Digital World resembles a vast blackish body of water, a beach with an empty town and a cave, and a lighthouse on the beach's shore.

History
The first appearance of the Dark Ocean chronologically was when Ken Ichijouji transformed his original Digivice into a black D-3 after having been infected with a Dark Spore sometime after his original mission in the Digital World.

Years later, Kari Kamiya found herself brought to this world, but was later rescued by Gatomon, TK, and Patamon.

After the reboot, Maki Himekawa ended up in the Dark Ocean and was presumably drowned.

Plot
The Dark Ocean has been a recurring location throughout the series. Its nature stands in stark contrast to characters intimately connected with the power of light such as Kari Kamiya and Maki Himekawa, who have both served as mediums for the Digital World entity known as Homeostasis.

Other characters such as Ken Ichijouji, who have been infected by darkness in the past also have a connection to this world. Due to his lingering connection to this world, with great effort, Ken is able to use his remaining dark powers to trap powerful Digimon who are able to travel freely between the real world and Digital World such as Daemon in this world.