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