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.
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.