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