Beltany Stone Circle stands on a hill near the village of Raphoe, about 14 kilometres south-east of Letterkenny. It has lost stones over the centuries but remains a clear circle of 64, with a central platform. It is probably much older than the Celtic festival of Beltane it is associated with, perhaps late Stone Age to early Iron Age.
It is free to walk up to at any time. Combine it with Raphoe's old Church of Ireland cathedral if you are heading that way.