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