The twin towns of Oregrund and Osthammar are closely linked geographically and historically. At the end of the fifteenth century, the citizens of Osthammar founded Oregrund in order to obtain a better harbour. Seafaring and iron-exporting became vital to the town. In 1719, Oregrund was burned by the Russians, but the wooden buildings were rebuilt according to a town plan from 1744. The Town Hall is from 1829.at the end of the nineteenth century; the sleepy area became a seaside resort and continues to attract visitors to this day.

The Oregrund and Osthammar region is home to many well-preserved old ironworking communities, including Harg and Gimo. Built in 1763-70, Gimo manor was the fist in Sweden to be designed in Gustavian style by Jean Eric Rehn.

Outside Gimo lies Skafthammars Kyrka, a medieval church particularly renowned for its lectern, which was built for the Gimo smiths.