I want something that really captures the feeling that you get in games like Shadow of Colossus, the Long Dark, games that make you feel small. The feeling of the sublime, that powerlessness and awe in the face of such a powerful force is something games can do so well.
As far as gameplay, one can just do Shadow of the Colossus x 100. A world inhabited by moving mountains. You're basically an ant walking, grappling, climbing and living on them, no way to kill them, very dangerous to lose your way on them.
Apart from the giants who rule the world, you'd also face elemental majesty, swirling vortexes of rain, wind, dust that will potentially wear you down to bones, or knock you off the giants. The fall wouldn't necessarily kill you, as whatever scattered civilisations that exist on this barren world would have developed means of surviving great heights, e.g. parachutes, grappling hooks, etc. But on the wasteland ground, you'd have to deal with not only getting accidentally stepped on by creatures with foot sizes of kilometres, but also the denizens of the ground.
These creatures, probably insectoid in nature ( they'd have to be, to be able to reproduce in large numbers and thrive in harsh environments ) would be your size, and the danger would be in being overrun before you can get away. So at least you'd at least have other survival/combat aspects to gameplay besides hanging on to some titan's armpit for dear life.