Grønligrotta Arctic Highway

The most accessible and most visited of the caves around Mo is 22km north of town. There's electric lighting (it's the only illuminated tourist cave in Scandinavia). The 30-minute tour takes you along an underground river, through a rock maze, then past a granite block torn off by a glacier and deposited in the cave by the brute force of moving water. If you're visiting outside high season, ring the tourist office in Mo to check timing.