Dun Ruadh is a one-off. Not quite sure what other term you would give to a massive horseshoe shaped cairn [still about 2.5 to 3m high - I reckon - in places] with a 17 stone circle defining a central courtyard. Apparently 13 cists were discovered in the cairn, some still visible, the whole site surrounded by a low bank and ditch......... so there you are.
Sited in the hills north of The Creggan visitor centre near Crouck - and featuring in its glossy brochure - the traveller is nonetheless on his own with this one - or at least you were at the time of my visit in June 2006, anyway. I therefore knocked at the nearest house, the woman who answered the door promptly 'ordering' her son, Brendan, to show us the way to the 'fairie ring' forthwith. 'Er, OK mam'. Right on! Needless to say we bunged him a few quid for his trouble and traded political viewpoints.... suffice to say we both have a distinct problem with bigots of all types and I hope I showed him a positive side to us 'Brits'... he was 16 at the time, but very clued up. I probably came across as a muppet, having said that.
Anyway the circle/cairn/whatever is a peach, very well preserved with great views of the Sperrins and bundles of atmosphere. Not surprising really, when only the locals know where it is and they can't understand why us crazy people want to go there. Long may it continue for this is one of Ireland's best.
Oh, and cheers to Four Winds for his web-site prompt.