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