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