Víðgelmir

thumb|right|Víðgelmir in Iceland - Expeditioners are walking on top of a "pipe" formed when half molten lava "skin" rolled down the walls when the eruption receded. thumb|right|Víðgelmir has many ice-formations deep within the cave. Víðgelmir () is a lava tube situated in the Hallmundarhraun lava field (formed around 900 AD) in west Iceland, around 2 km southeast of Fljótstunga farm in Hvítársíða, Borgarfjörður. The roof of the lava tube has collapsed, creating two large openings near its north end which are the only known entrances. Víðgelmir is 1585 m long and the largest part of t