Complex sentence: The clanking of hammers echoing off the walls and low, narrow cave passages are two things a visitor will likely remember... as well as a bump on the head if he or she forgets just how low those passages are.
Split into simpler sentences: The clanking of hammers echoing off the walls and low, narrow cave passages are two things a visitor will likely remember. As well as a bump on the head if he or she forgets just how low those passages are.