The finest chambered cairn in northwestern Europe, Maeshowe was built around 2800 BCE — older than Stonehenge — and is a marvel of Neolithic engineering. The long entrance passage is aligned so that on the days around the winter solstice the setting sun shines straight down it to illuminate the rear wall of the chamber. The chamber itself is built of vast slabs of sandstone, some weighing more than 30 tons, fitted without mortar.
Visits are by guided tour only, booked in advance through the visitor centre at Stenness. The site is small and tours sell out, particularly around the solstice. Allow an hour including the tour. The Viking runes on the chamber walls are pointed out by the guide.