The trickiest part is learning how to "mine-and-sidestep" on blocks 12 and 18. I've noticed that having a fast or unclogged computer helps.
1-3: Break through the blocks of dirt and glass. alternatively dig through the dirt and break the softstone (saves 1 energy
4: Pick the gold key.
5-11: Burrow through these dirt blocks.
12! Get ready for some quick-feet action:
Start breaking 12 just after an arrow passes by. As soon as 12 breaks, move to the right to avoid the next arrow. Continue to 13, timing your moves to evade the arrows.
13-16: Open the door, build a bridge, chop up 15 and pick up the copper arrow.
17, 18: Get back to the central chamber, bust 17, repeat your quick moves at 18, carefully evade arrows and move on to 19.
19-23: Open the door, destroy the softer blocks at 20 and 22, while making short work of the purple blob at 21. Pick up the silver key.
24-28: Move on to 24, unlock 25, chop up 26 and unlock 27. Loot the chest at 28.