Situated in the Ódáðahraun lava-field, Trölladyngja is the biggest of the Icelandic strato-volcanoes, reaching a height of 1,468 meters above sea-level, and rising almost 600 meters above the surrounding desert and lava-fields.

It's about 10 kilometers in diameter, it's inclination is 4 - 5° in the lower slopes, but 6 - 8° higher up. It's oblong crater is about 1,200 - 1,500 meters in length, 500 meters broad, and about 100 meters deep.

Most of its lava-fields have flowed in a northerly direction, with one branch of it reaching the valley of Bárðardalur, a distance of roughly 100 kms.