Lava Show is a compact indoor attraction built around live, superheated lava poured in front of the audience. It is clearly staged, but in Vik the subject feels earned: black beaches, sea stacks, glaciers, and volcanoes are all part of the same south-coast story.
Go if bad weather has pinned you in town, or if you want a close look at lava without pretending that a natural eruption can be scheduled.