Wideford Hill Cairn is a 5,000-year-old chambered tomb above Kirkwall, and it has the special Orkney quality of feeling both prehistoric and very close at hand. The cairn is well preserved, with a central chamber and side cells that make the engineering easy to grasp once you are inside.
Access is part of the experience: the walk can be muddy and the modern entry is through a roof hatch and ladder. Bring a torch, wear boots, and combine it with other Mainland Orkney sites if you want a day that moves from open views to enclosed Neolithic stonework.