All of Wales?
You need to be more specific. While Wales may look small it is a fair distance from north wales to south wales, and travellling from north wales to south wales is not easy due to many mountains in the way and few major roads.
I would decide on either North Wales or South Wales and concentrate on one or the other.
North Wales has Snowdon, Snowdonia, Llandudno, Rhyl, Lynn Peninsula, numerous castles (Harlech, Carnarveon, Conwy) etc.
South Wales has Cardiff, Swansea, Pembrokshire coast (beautiful), Gower Peninsula (beautiful), St Davids etc
Once you have decided on one or the other then ask again.