"Kverkarhellir cave is a deep artificial cave that was dug out of soft rock. New research indicates that construction on it began in ca. AD 800, nearly 70 years before the Vikings are believed to have settled Iceland.
Seljalandshellar cave is a three chambered artificial cave located near Kverkarhellir. On its walls 23 carvings of the cross have been found. A typological analysis reveals that they are similar to crosses drawn in western Scotland in AD 800 and earlier."