One of the problems is that Wales and 'chocolate box villages' don’t really go together...although there are lots of castles!
Your main problem will be public transport as this will limit what you can do .
Some ideas to get you started...
Cardiff would be a possible. Not only does it have an impressive
castle, there is also the wonderful
Castlell Coch on the edge of the city and reachable by bus. With its turrets this is everyone’s dream of a fairy tale castle. Just a short train ride is
Caerphilly Castle, one of the great ruined medieval castles
These would make three very different visits.
Also a short bus ride from Cardiff is
St Fagan’s National Museum of History. Old buildings from across Wales have been moved and rebuilt here. It is a real step back into the past. There is so much to see, you could easily spend a full day here.
Pembrokeshire is wonderful but one problem is many areas have poor public transport.
Tenby is a very popular holiday resort which has a station. It has the scant remains of a ruined castle as well as town walls.
Caldey Island is just a short boat trip away.
North Wales - think about Conwy or Llandudno. Both are on the railway. They are only a few miles apart and there is an excellent bus service between them. LLandudno has more choice of accommodation.
Conwy is an attractive walled medieval town still with its original street layout, with a ruined castle as well as
Plas Mawr, which is described as one of the best Elizabethan Town Houses in the country.
Llandudno is a Victorian sea side town with pier, long sandy beach with a promenade and an old fashioned
Punch and Judy show. It also has the
Victorian Tramway to the top of the Great Orme
or take the
vintage bus ride along the Marine Drive and to the top of the Great Orme.
There is also a regular bus service to
Caernarfon (see #6 & 7 with its ruined Castle.
Betws y Coed is a very pretty village just a few miles up the Conwy valley from Conwy and can be reached either bus or train.