Studied my undergrad degree in Cardiff University. I spent most of my 2 first year at home or uni, it wasn't but until last year that I decided to explore around. Brecon Beacons is obviously one of the first destination is your are anywhere around Cardiff. I stayed in a little town called Brecon as far as I remember. For 2 days we went hiking and going back to my hotel/pub to get some drinks. Locals are extremely friendly although their accent was surprisingly hard to understand. The highlight of the trip was Pen Y Fan. One of the biggest mountains in South Wales (probably not). Great climb, took me around 3 hours with constant stops to check the view and get my tripod set. Definitely one of the best places to visit, not far from Cardiff but I do recommend to stay in one of the little towns inside the natural reserve. It is way more convenient to hike around, specially if you don't have a car. They are also cheaper. You can get a bus from Cardiff every couple of mins.
All photos taken with the Nikon D90 and Nikkor 50mm F1.8G. Edited with Lightroom.