dark rock wall in an old deep well in the catacombs

arcane backstop barricade barrier belowground block builtin calculus catacombs clandestine cobble cobblestone concretion covert crag craggy deep defense defenses design drawwell fortification fountain furtively hard hedge ironbound mural paries partition pattern paving pebble petrous privily quay rock rockribbed rocky roll roller rubble scale scar scaur secret shaft side solid spindle stone stony strong sturdy subterranean subterraneous sump texture tracery tube undercover underground wall weave well