In the land of Efra-Hvol you can find three man-made caves collectively called Efra-Hvolshellar, which translates as Upper-Hvol Caves. They are dug into a rather coarse breccia that likely originated from tillite deposits. The lower part is finer grained showing a combination of layered and cross-bedded sandstone. Two of the caves are joined together with a short tunnel and are called Top Cave and Center Cave, while the third is called Big Cave and is believed to be the 2nd longest man-made cave in Iceland, measuring some 45 meters in length. No remains of human activity have been found in the caves, but as of yet no research has been done on their history or how they were used. During the early 20th century, the caves were used as a sheep house and a barn but since 1943 they have not been in use and have been protected as a natural site since 1929.
A part of the roof of Big Cave collapsed and filled in the cave, but in consultation with the Cultural Heritage Agency of Iceland, the cave has now been partly dug out so it can be visited but please be careful as the ceiling might be unstable in parts. The access to the caves is good and should be easy for most people to visit them. There is a car park close to the caves with about a 160 meters long trail leading from the carpark to them. There are some steps leading to the caves that are steep so please be careful there. The caves tend to fill with snow during the wintertime, so they are not always accessible.
The caves are just outside of the town of Hvolsvöllur and are well marked. To get to them you need to turn of Road 1 onto road 261 in Hvolsvöllur. You follow that road out of the town and then turn left onto road 262. Then you drive about 2 km and make a right-hand turn to the farm of “Þórunúpur” (is marked “Efra-Hvolshellar” as well) and follow that road for a short while until you get to the car park for the caves. The area around the caves is beautiful and there is a bench there where one can eat a packed lunch. Please do not leave any trash behind there and keep in mind that dogs must always be on a leash there.