25 miles, with plenty of carrying!
Mourne Wall Starting Point Multimap Link
Get yourself a map of the Mournes for this one (OSNI Discoverer Map 29), be careful, and apply some common sense in terms of which bits to ride!
Park in any of the car parks shown on the map, and off you go, starting with Slieve Muck! After summitting Muck, head North to go round the crags - do NOT head over the edge!