So I wish to start this off in an underground place, be it a crypt, a tomb, whatever. This'll begin with two characters who've known each other for a long time, and they've just retrieved some kind of artefact from this place. They find a door behind where they found the artefact, and it reacts to this door, opening it. They push it enough to see what's behind... Only to be swept into darkness. Waking up, the two find themselves in a world where they can see only themselves, for now at least. The absence of light is terrifying, but, as time goes on, they realise they're within a place made up of black crystal. It's from here where we begin plotting and the like.