2 Best Sights in Reykjanes Peninsula and the South Coast (with the Golden Circle), Iceland

At 1,360 meters, the Lava Tunnel is the fourth-longest lava cave discovered in Iceland. The cave is remarkably spacious—from 10 to 30 meters wide and up to 10 meters tall—making it quite easy and accessible for most people. Walking along the lava's 5,200-year-old path is a humbling experience in itself, and the views of the geological formations and spectacular colors are extraordinary. In winter, big crystal-like ice sculptures form inside the cave entrance. The standard Lava Tunnel tour takes about an hour.

Ancient crosses, wall carvings, and carved seats decorate twelve mysterious caves outside of Hella. Filled with historical remains, they have only recently begun to be excavated—and researchers already think they might predate the Vikings. Four are currently open to the public, but take note that you're only allowed to see the caves on guided tours, which are offered in English every day at 12 and 4 pm.