Not far from Doagh, in Co. Antrim, there's a Neolithic standing stone with a hole in it. It is imaginatively known as the Doagh Hole Stone. There aren't many like it. There's a similar one in Galloway, which I've seen, and I believe there's another one in Cornwall which may be worth a visit. Apparently the hole is narrow enough for most women's hands to pass through it, but not most men's hands. I didn't try.