Step 1: Go to the surface.
Step 2: Press 'end' to level with the horizon.
Step 3: Hold down 'F' while moving around.
Step 4: Enjoy your hike!
Or just point a bit towards the ground to keep you there. Or use airplane mode and let gravity keep you on the ground.
Space Engineer did show some ground based models that he was testing out (not present in the current version, AFAIK), so we could see a ground mode or something.
so if u could run around what ever world. at the speed of light.
You'd have to be a few kilometers up to keep from smacking into the landscape with the way things work currently. Besides, your computer would crash from trying to load everything.