Caving
From The Blockheads Wiki
To keep track of which tunnels you've explored or stripped of resources place a block of limestone at the entrance(s). It looks different than un-mined limestone so you'll know you placed it as a signal. You could also wall it off with stone because it is abundant. [File:Limestone_marker.png|thumb|300px] [File:Walled_off_tunnel.png|thumb|300px]
