An enclosed area of older bedrock in the eastern part of the Ögmundarhraun lava flow south of the main road. Such phenomena is referred to as puka in the geological literature. The Ögmundarhraun lava flow is historic and formed in an eruption in the year 1151 AD. In this enclosure are ancient ruins which are older than the lava flow. There are two earthworks which the lava flow has partially submerged and one of them has been dated older than 871 AD and thus one of the oldest man-made structures in Iceland. In small outliers on its western are ruins of farmhouses which the lava has encircled and partially overrun. This place has been referred to in the past as Forna-Krýsuvík (i.e. The old Krýsuvík). It is thought that the original Krýsuvík farm was located there but after the eruption it was move further to the northeast.
Óbrennishólmi is a enclosure of older bedrock within the Ögmundarhraun lava flow from the year 1151. In the enclosure are ancient ruins. One is a circular sheep fold and close by is an earthwork (turf wall).
Haukur Jóhannesson, 2010