The Clava Cairns are a set of Neolithic stone structures about a mile from Culloden Battlefield in Scotland. Three burial cairns, two of which are passage graves. You can go inside (the first photo is of me inside looking out.). There is a nearby circle of standing stones, liked by lines of turf-covered stones. Several of the stones have cup and ring marks inscribed on the stones, the purpose of which no one is certain.
One of the standing stones is split in two (third photo), and was the inspiration for the split stone in the novel Outlander, now made into a television series.
You can read this and more in my ebook on Scotland: Stunning, Strange and Secret: A Guide to Hidden Scotland.