In reply to pasbury:
If you're starting in the north begin from Maentwrog and follow the Ceunant Llennyrch gorge, through the "Celtic Rainforest" to the dam at Llyn Trawfynydd. https://www.geograph.org.uk/photo/3789961
From there head on to the weirdness of Craig y Gwynt, then Moel y Gyrafolen, then traverse the badlands over mini canyons and rocky slabs to Moel Ysgyfarnogod, then Clip. Detours to some of the small lakes round here are worthwhile. https://www.geograph.org.uk/photo/3897074
From Cwm Bychan you're then onto the main ridge proper.
A worthwhile but time-consuming detour would be to Y Garn, a summit to the east with views over the Coed y Brenin. If you like waterfalls, head down from there to see the Rhaeadr Ddu on the Afon Gamlan.
*edit* I just see you said starting in the south. Oh well...But in which case the scramble up the south side of Rhinog Fawr is mildly diverting. It got g3 in the Scrambles and Easy Climbs book, but is mostly g1 and avoidable.
Post edited at 10:08