What is "torsburgen"

Torsburgen, Tors borg or þors borg ("Thor's fort/castle") are the remains of an ancient hillfort in Kräklingbo on the Swedish island of Gotland in the Baltic Sea. The fort is approximately , was constructed in the 1st-4th century and in use until the 12th century. Situated on a plateau hill it is protected by high cliffs and wall sections, almost long in total. The fort is featured in the Gutasaga. The plateau is also a nature reserve.