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