You can have a nice hike around the Marchlyn Mawr reservoir. You will not go up any of the big name mountains in North Wales but you can see them all.

On the ascent via Carnedd y Filiast you can see the the Carneddau mountain range and Nant Francon. A bit further on you can see all the Glyderau mountains (Foel Goch, Y Garn, Glyder Fawr) and once you are up Elidir Fawr (924m) you can see the Llanberis valley and the Snowdon range and over to the Llŷn peninsula. The whole tour you have really nice views of Anglesey and on a good day you can even see the Isle of Man.