Photo from The Lava Tunnel | Raufarholshellir Caving Tour
Raufarhólshellir is the fourth longest lava tube in Iceland at 1,360 metres (4,461 ft). It is also remarkably spacious, between 10 and 30 metres wide (33 to 99 ft) and up to 10 metres tall (33 ft).
One of the closest caves to Reykjavík, it is accessible throughout the year on sanctioned tours. It is also accessible to more people than caves such as Leiðarendi, as it requires no crawling or clambering to get through. Even so, the ground is uneven, thus people with back or knee problems should consider entering it carefully.
Though the standard tour is good fun, those who seek a more adventurous tour can take a four-hour excursion in which you plumb the cave's depths.
Raufarhólshellir is one of the best places in Iceland see the effects of the subterranean forces at work in such a volcanically active country. The textures and colourations of the rocks, for example, are as beautiful as they are fascinating.