A game set in a world with no sun. You are in perpetual darkness. The only thing that provides light are special stones that occasionally jut up from the ground...but they don't last forever. You can either explore the darkness on your own, or with travellers like you that you come across, or you can set up a town around a large light providing crystal, and defend against the hulking, nightmarish horrors lurking just past the edge the light. In order to build you have to go out and hunt ever more powerful creatures and harvest their skin, flesh, and bone to make buildings, weapons, and equipment.
Youd have to include grappling/climbing mechanics similar to Shadows of the Collosus. The game needs to be permadeath. You can't savescum the boss fights in order to win. Fights need to be terrifying and intense....and when you win...the feeling would be indescribable.