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