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