Eldborg is a beautifully formed volcanic crater that can be seen from road 54, rising 60m above the surrounding land.
Known as a lava spatter ring, the symmetrical crater is believed to have formed 5000-6000 years ago in a gentle, effusive eruption that built up its steep walls from lava spatter.
According to medieval chronicles, there was a further eruption in the area, around the time of the settlement of Iceland, but that eruption came from another site, though one which is also part of the large volcanic system Ljosufjoll.
Access to the crater, which is 200m in diameter, is from Snorrastadir farm along a 2.5km trail taking about an hour each way. Snorrastadir offers horse riding along the stunning Longufjorur beach.