Separate trips, CS3.
There are two classic horseshoes:
The classic is the central horseshoe from Neuadd Reservoirs north of Merthyr Tydfil. Cross the reservoir dam and ascent Craig Fan Ddu and walk north to Bwlch Duwynt, continue over Corn Du, Pen y Fan and Cribyn, and continue on to The Gap where you can take the track back down to the reservoir. Alternatively, continue over Fan y Big and follow the escarpment round, turning south onto Craig Fan Las and Craig y Fan Ddu before returning to the reservoirs via the Taff Trail.
The 'other' (with apologies to Impy Dave) is the Llanbedr horseshoe from Llanbedr just north of Crickhowell. Ascent Table Mountain, then head north to Pen Cerrig Calch and Pen Allt Mawr, continue over Mynydd Lysiau and Pen Trumau before turning east to Waun Fach. Then turn south, taking in Pen y Gadair Fawr, Pen Twyn Mawr and Crug Mawr before descending south west on the public footpath back to Llanbedr (nice pub).
There are various Waterfalls Walks. The best, imo, is this one: Waterfalls Walk 
