Thrihnukagigur Volcano, located near Reykjavík, Iceland, is a dormant volcano that hasn't erupted in over 4000 years. Discovered in 1974, it's unique because visitors can take an elevator down into its magma chamber, which is massive and awe-inspiring. The magma has mysteriously drained away, revealing the underground rift. It's so cool that even the band Kaleo recorded a live performance inside the volcano!