Not sure if this one has been mentioned before, 120 miles of a run with amazing scenery in the SW of Ireland, near the famous Ring of Kerry Road.
http://www.kerrywayultra.com/
Would involve a circuit of the Reeks and Dunkerron mountain ranges, starting and finishing in Killarney, with everything from stretches across upland bog to oakwoods over mountains and valleys down to the Atlantic Coast. Spectacular setting.