Cardiff is a vibrant city, with plenty to do in the way of shopping and museums (try the National Museum of Wales and the Turner House Gallery. Most of the city centre is pedestrianised, and the buildings tend to be in a Victorian or Georgian style with some swanky new areas such as The Docklands and Cardiff Bay. There are also trendy bars aplenty on Mill Lane. The north of the city is industrial and grew up around the famous Welsh coal mines. The city is definitely small enough to walk around.
The Welsh Capital is well situated for travel. The airport has both domestic and international flights, the M4 takes you direct to London and there are train links throughout the UK most notably the easy journey (30 mins) across the water to party mecca Bristol.
Now the important bit:
Unusually for a city university Cardiff has it's own unofficial student village situated in the Cathays area. Private accommodation, but might as well be a campus as it's all students. This means there's a campus-like atmosphere in the very centre of the city. Among the great bars to choose from try: The City Social, Molokos, HA HA's! and The Yard which have a late licence on many nights. The general theme of these pubs/bars is lively/studenty with prices not that much more than the Students' Union.
Clubbing-wise the scene has been developing rapidly for the last few years and there's something for every clubber. For a casual and stylish cluber out for late night drinking and partying the all new Tiger Tiger is the best option with music for all tastes. For the commercial clubber Creation provides the thrills. For the hardcore student night Liquid and Bounce are ideal.
There are plenty of bars with dance floors and late licences, too numerous to mention. For the cheapest beer in town head to The Prince of Wales, the local Weatherspoon. For something a bit different Bar Cuba is particularly popular with international students.
Verdict: Friendly atmosphere, top notch clubs and great bars to rival great towns such as Manchester, Birmingham and London