Splendid searfaring fantasy-horror roguelikelike Sunless Sea [official site] is already set down in the dark, sailing oceans long ago swallowed by the earth. If that’s not terrifying enough, imagine what lies beneath those waves. I bring good/bad news!
Developers Failbetter Games are planning to let you get up-close and personal with what lies under the Unterzee in the game’s first DLC, named Zubmariner. As you might guess, it involves submarines. Details follow.