thisa is really neat. i have been currently working on a titan tunnel, hollowing out an entire world, starting last october with my kid. it really started out with attempting to drain an oceanfront, from there it spiraled into a really big pit with completely unnecessary load bearing walls (i computed nearly 600,000 removed blocks just for the pit), then a tunnel. Battling lava is the real big challenge, as well as glitch spots that cause me to run up against invisible blocks that cant be dug or bypassed.