Víðgelmir

Víðgelmir (Icelandic pronunciation: [ˈviðˌcɛlmɪr̥]) is a lava tube situated in the Hallmundarhraun lava field (formed around 900 AD) in west Iceland, around 2 km southeast of Fljótstunga[1] 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.

An iron gate was installed at the first constriction in 1991 to preserve those of the delicate lava formations or speleothems which hadn't already been destroyed.

Evidence of human habitation, probably dating to the Viking Age, has been discovered in the cave and is preserved in the National Museum of Iceland.

Long stretches of the cave floor are very rough and shouldn't be navigated without a guide.

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.
Víðgelmir has many ice-formations deep within the cave.