If you like walking, there are the Preseli Mountains, which I think is about 7miles in total (could be wrong). Then there is the coastal path.
History wise, there is Pentre Ifan (Burial Chamber), there are castles like Carew, Cilgerran, Llawhaden, Picton, Pembroke, and there are loads of smaller ones. There is a wildlife centre in Cilgerran - it's a trail with hides to watch the birds, water buffalo and otters. There is Castell Henllys. There is also St David's Cathedral, which is in a lovely little place and plenty of places to get food. Mwnt is nice, but it is narrow roads to get there.
For beaches, whitesands is not far from St David's and is nice, there are many beaches around. Tenby beach is usually very busy but nice. Saundersfoot is lovely but the carpark can be expensive so can the food.
If you head into Cardigan, Pendre Cafe (Fish & Chips - Freshly Cooked) is the one I would recommend, it is on the high street. Gwbert is not far from here, you can sit and look over the water. Fishguard and Goodwich is ok. There is a harbour in Goodwich (large carpark), there is the Ocean Lab, which does lovely food. If you are just looking for a nicely cooked lunch, you could try Caffi Becca in Efailwen (not sure if you have to ring up and book).
There are so many different places. Hope this helps.
Sorry about the spelling. I think I got carried away 