Machrie Moor - because it has everything you could need - trek to get to, nice walk, and an example of pretty much most types of circle.

http://www.themodernantiquarian.com/site/161/machrie_moor.html

Stenness - a site that I literally had to be dragged away from, just so beautiful, and it's neighbouring monuments aren't bad either.

http://www.themodernantiquarian.com/site/389/standing_stones_of_stenness.html

Drizzlecombe - other half is from Dartmoor, but had never heard of it. Just so much there to see, from when Dartmoor was civilised.

http://www.themodernantiquarian.com/site/1371/drizzlecombe_megalithic_complex.html

Can I add an honourable mention for Scorhill (in the snow), Lligwy and in fact all the Anglesey monuments, Rousay sites (double-decker burial chamber, and the biggest chambered cairn you'll ever see). Generally. most sites on islands. And hunebedden.

God I wish I'd never bought this book, and found the website. Might have gone on normal holidays like normal people. To Ibiza, rather than a tent in Mull in the rain.

Sam