Duddo stone circle is superb and well worth the journey,
Joolio
...and on the way up to Duddo there's stacks of Rock Art to see, varying in accessibility.
Check out the postings for these for starters:
Weetwood Moor - Most value for effort http://www.themodernantiquarian.com/browse.php?site_id=2915
Routin Linn - v. famous, in a little wooded area, and not far from Duddo: http://www.themodernantiquarian.com/browse.php?site_id=96
Chatton Park - wonderful views on a clear day http://www.themodernantiquarian.com/browse.php?site_id=3075
Kettley Crag - just over the hill from chatton and my personal favourite: http://www.themodernantiquarian.com/browse.php?site_id=3076
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