Sunless Seas currently free on the Epic Store. I have no idea what it is.
Oh, it's a spin-off rogue-simulator where you control a steam-ship as it traverses an dark ocean under the surface. You home-base is the haven of London, it has a lot of plotlines, and depending on what path you chose, you get different stories. It is very difficult the first times, and the game recommends accepting that your first captains can and will die while you try to get the hang on gameplay.
I recommend it if you are a fan of ztrange zee-ztories and zailing the zubterran zee.
EDIT: There's also an expansion which allows you to build a zubmarine with which you can explode the underzee too.
Just be prepared for a Constant Companion.