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