You walk down a cold hallway, a mean, weary light glinting off the stained metal floors and bulbous organic matter clinging to the floors and wall. You are wearing a dense and cumbersome suit, its many functions obscured by thick ridges of armored plating. Your curved helmet leaks a subtle glow from the slatted visor, the data it overlays over the corridor before you providing a numb comfort through facts: you have this much life support left, this much ammunition remaining in your weapons.
There are things waiting for you ahead in the dark and the quiet: horrible, sharp things that want you dead for no other reason than you are there. It's bad enough that they're there waiting, bad enough that you have to fend them off in hordes as you plumb deeper into this wholly other place, but nothing is more terrible than the distance between you and Earth.
You move forward, checking corners for precious supplies and upgrades, because you have no other choice. Because those are the rules.