Image: Pétur Reynisson
Reaching the bottom
Thrihnukagigur has lain dormant for the past 4,000 years – since long before humans arrived on Iceland. It was first discovered in 1974 and was fully explored and mapped out in 1991. Entry into the magma chamber is via a 13×13-foot (4×4-meter) opening. The chamber then drops down 394 feet (120 meters) below the surface. The crater itself is bottle shaped and its cave a whopping 5,300,000 cubic feet (150,000 cubic meters) in size.