As said, a lot of the things ‘to do’ in Wales are getting out and enjoying the countryside.
If you are in to nature/wildlife:
– Look for dolphins off the New Quay to Cemaes Head coast (e.g. Ynys Lochtyn, Mwnt) walking along the coastal footpath.
– If you get far enough west visit the puffins at Skomer/Skokholm or from the Stacks off Anglesey.
– Both the Anglesey and south-west coasts are fantastic to try out sea kayaking.
– If you’re staying around Tenby/Saundersfoot you can look for otters, owls and bats at dusk at Carew Castle.
Heading north to south on the coast, this campsite is great, right on the coast, middle of nowhere, but might be busy if its the school hols. You can bike round the foothills of Cadair Idris from the site if you’re fit.
If you like solitude, the Berwyn mountains are very remote and not at all touristy. Pistyll Rhaeadr is the tallest single drop waterfall in the UK. I have been recommended this campsite by friends, on the River Dee in Carrog, over the bridge to a pub, and 10 mins drive the Pontcysyllte Aquaduct, which I would also recommend seeing if your passing.
To be honest, I could spend 2 weeks in just one bit (Anglesey, Snowdonia, Pembrokeshire)… as long as the weather’s reasonable!!