After learning his property straddled Kazumura Cave – the world's longest lava tube – Harry Schick tirelessly worked to become an expert on this geologic phenomenon. Although 20 years of tours has made his delivery a bit rote, the abundant information and unique sights still make for a fascinating adventure. The recommended four-hour tour ($50) culminates with the appropriately named Wow Formation.

Be prepared to climb ladders and walk over loose, rocky terrain, even on the shortest, easiest tour. Minimum age is 11 years. Group size limited to six people. Make reservations at least a week ahead; directions to the site are given upon reservation.