Callanish Stone Circle at Dawn, Isle of Lewis, Outer Hebrides, Scotland (photo by Patrick Dieudonne). Neolithic stone circles are definitely on my bucket list. fellow Diana Gabaldon fans will understand, I'm sure.
Viking ring fort and settlement, the Shetland Islands, Jarlshof, Scotland. It has been described as "one of the most remarkable archaeological sites ever excavated in the British Isles". It contains remains dating from 2500 BCE up to the century CE.