Reykjanes is riddled by a subterranean network of lava tubes, formed when the sides of a deep lava flow cool and solidify, allowing the still-liquid centre to drain away after the eruption ends. Pick of the local tubes include kilometre-long Raufarholshellir; the similarly scaled Buri Cave, only discovered in 2005; Þríhnúkagígur, though this is actually a drained magma chamber; and Leiðarendi, perhaps the most accessible. With the exception of Þríhnjúkagígur, you can only visit these as part of a tour offered by extremeiceland.is (9500–25,000kr/person).

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