The Zubmariner Add-on for Sunless Sea has 24 achievements.
Be killed by an underwater creature
Die of suffocation
Avoid being killed by the Unexploded Unclear Bomb
Accept a power of the deep zee
Complete the Zubmariner ambition
Perform an abyssal ritual to encounter Lady Black
Be killed by the Constant Companion
Collect all of Drownie Love-song, Drownie Counterpoint and Drownie Hymn
Come face to face with the Constant Companion
Discover Undercrow
Discover Nook
Discover Scrimshander
Discover Hideaway
Discover Aigul
Discover Dahut
Discover Rosegate
Use an oasis to increase your oxygen levels
Discover Wrack
Escape underwater combat by resurfacing
Discover Low Barnet
Discover Anthe
Discover The Gant Pole
Use underwater currents to bear you on your way
Venture beneath the waves