Caving · Southwest IcelandLava tube caving, RaufarhólshellirADVANCEDRisk: MODERATEEUR Adventure tour ~150–200One of Iceland's longest lava tubes, formed by a flowing river of molten rock roughly 5,200 years ago — beyond the lit tourist boardwalk section, guided "adventure" routes head into unlit, technical passages requiring scrambling over collapsed rock and squeezing through narrower sections.View details