Kind of depends how much further afield your willing to go. If you can pop over Dollgellau sort of way (old county of Merionedd) there's a cracking mountain called Cadair Idris with the most stunning set of lakes at Llynnau Gregennan. Stones dotted around near it too. Theres pretty good info on TMA. Dollgellau could take a bit over an hour from Newtown, mind you, think it depends how you drive!! And of course, if I'm thinking of the right Newtown, could of got things arse about face as usual!!.
Have fun though, very jealous.
Blaidd