Hekla is a volcano located in the south of Iceland with a height of 1,491 metres (4,892 ft). Hekla is Iceland's most active volcano; over 20 eruptions have occurred in and around the volcano since 874. During the Middle Ages, Icelanders called the volcano the "Gateway to Hell." It is only 45 minutes drive away from Geysir.

Hekla is part of a volcanic ridge, 40 kilometres (25 mi) long. However, the most active part of this ridge, a fissure about 5.5 km (3.4 mi) long named Heklugjá, is considered to be the volcano Hekla proper. Hekla looks rather like an overturned boat, with its keel being in fact a series of craters, two of which are generally the most active.

The volcano's frequent large eruptions have covered much of Iceland with tephra and these layers can be used to date eruptions of Iceland's other volcanos. 10% of the tephra produced in Iceland in the last thousand years has come from Hekla, amounting to 5 km3. The volcano has produced one of the largest volumes of lava of any in the world in the last millennium, around 8 km3. In Icelandic Hekla is the word for a short hooded cloak which may relate to the frequent cloud cover on the summit. An early Latin source refers to the mountain as Mons Casule.