Lava Tunnel Raufarhólshellir is one of the longest lava tubes found in Iceland. The tunnel is located just 30 minutes from Reykjavík. The tunnel was formed during a massive volcanic eruption, which occurred around 5,200 years ago. Visitors can see evidence of this eruption in the form of stunning lava decorations such as stalactites, stalagmites, and lava walls that line the tunnel.