Broch of Mousa, Shetland
This is an Iron Age style broch, which was built round about 100 BC and it the tallest of all brochs, as it still preserves its full structure, save the (likely thatched) roof. In fact, it is one of the best-preserved prehistoric buildings of Europe. It is situated on the Island of Mousa, which is now uninhabited, and it can only be reached by boat, which operates between April and September. Storm petrels, European shags and seals can be seen on the island, as well as, a beautiful rugged coastline.