Seamless (Ludum Dare 48 #29 entry)
A / left arrow to start walking left
D / right arrow to start walking right
S / down arrow to stop
Where there's muck there's brass, so get a shift on and head down the mineshaft to coalface number 4 and get drilling.
(Much like the South Yorkshire coalfield that inspired it, this is a bedraggled shadow of what might have been, built on the bones of something much bigger. I ran out of time in the 48 hour competition, so there isn't much in the way of gameplay at this - once you've made it to the drilling machine you've seen pretty much all there is to see, except for some fairly spectacular physics glitches.)
UPDATE: Minor bug fix made post-compo to make the tunnelling a bit more stable, but you may still fall off the edge of the map!