I liked my trip to the Plague Market (written up on TMA here) with its little stone circle, menhir, hut circles, cist and two stone rows! also v accessible but quite quiet nonetheless.

If you want to see some absolutely mad trees dripping with long lichens you should go to Wistman's Wood - a walk north from Two Bridges. It's the only bit of ancient woodland remaining on Dartmoor (mostly because it's growing on mad mossy boulders and so couldn't be grazed) - but look out because it's where the devil kennels his red-eyed hounds.

have fun - hope it's sunny for you