Raufarhólshellir, the Fourth-Longest Lava Tube in Iceland

Raufarhólshellir runs nearly 1,360 metres (4,500 feet), which makes it the fourth-longest lava tube in Iceland, and the lava that cut it moved through here more than 5,000 years ago. The walk inside covers about 350 metres (1,150 feet) of that, on wooden staircases and walkways built through the cave, and it takes an hour. Helmets and torches are handed out at the entrance. What the lights pick up is colour. The minerals in the rock have stained the walls in bands, and the guide explains what put them there. One section of the cave was used as a location in the film Noah, with Russell Crowe and Anthony Hopkins, and it is recognisable when you reach it. The meeting point is the BSÍ bus terminal in Reykjavík, and the whole thing, transport included, takes three hours.