A visit to the Broch of Gurness first, then from the mainland across the causeway to the island in the Bay of Birsay. The island across the causeway has the remains of several Norse long houses, and the remains of a chapel, compete with red sandstone block altar. You can only cross the causeway to low tide, and there’s a modern concrete walkway which has been put in to aid travel. Otherwise it would have been somewhat of a scrable over the rocks before the tide came back in. There’s a two hour gap every day in which the island in accessible, so perfect for an isolated community.