There isn't enough room on this page to list all the potential dangers in some of these old mines. I live in Washington and we have hundreds of these old mines. Just about everything imaginable was mined out of these mountains, gold, silver, coal, copper, lead, mercury and uranium to name just a few. The dangers including such things as "bad air" (little or no oxygen in the air), cave-ins, unstable tunnels, whizzes (vertical shafts within a horizontal shaft) rotted timbers for shoring/bracing, etc... I never go in one without a partner and always leave an additional partner at the truck with a good radio or satellite phone, serious first aid kit, and basic life support and first aid training. Always take a good light and extra batteries. it 's not a bad idea to lay down a line of string or rope from the entrance for a guide to rescuers if needed. We always set a definite return time and keep it. If we are not back within 15 min. of the set time the man at the truck notifies rescue and waits for them at the entrance. Just remember you can't be too careful when entering these old mines.Good hunting!!