In reply to TheDrunkenBakers: A full traverse of the Glyderau is good. Up from Bethesda to Carnedd y Filist then over Mynydd Perfedd (optional out and back to Elidir Fawr) - Foel Goch - Y Garn - Glyder Fawr - Glyder Fach (optional out and back to Tryfan) - Y Foel Goch - Gallt yr Ogof - Cefn y Capel. Down to Capel Curig for a pint.
A full traverse of the Snowdon range. From Beddgelert to Craig Wen - Yr Aran - Snowdon - Garnedd Ugain - Moel Cynghorion - Foel Goch - Foel Gron - Moel Eilio.
Or something in the Moelwyns. Ffestiniog up to Moelwyn Bach - Molewyn Mawr - Moel yr Hydd - Allt Fawr - Moel Druman - Ysgafell Wen - Moel Meirch - Carnedd y Cribau - Moel Siabod, and down to Capel Curig. That passes some very varied terrain.
All these are linear, but feasible with two cars/a bus/hitching a lift.