Mine shafts and portals are often hidden by vegetation or decaying boards, and can be hundreds of feet deep.
Horizontal mine openings may appear to be safe, but are prone to cave-ins and are home to poisonous snakes. Pockets of deadly odorless gases, darkness, hidden vertical shafts and rotten roof support beams all add to the danger, and endanger the people who are called to rescue you.
Old explosives at abandoned sites are very unstable and can detonate with a slight touch. Blasting caps resemble a firecracker with wires and can explode if stepped on.
Click this link to see pictures of dangerous mine openings.