Arround the immediate vicinity:
If you fancy venturing outside Cardiff you will find excellent road links and many interesting places to visit and see such as Castell Coch, a romantic fantasy - a piece of Bavaria imported into the Cardiff valley. It clings dramatically to a hillside overlooking the Taff river. It is especially dramatic at night as you drive past Cardiff on the M4 and you see it illuminated above you. Also a must is Caerphilly Castle. This vast, 30-acre fortress is only equalled in size by Windsor Castle and dates back to the 13th Century, the oldest Norman Castle in the UK.
Also just outside Cardiff you can find the Museum of Welsh Life at St. Fagans. This open-air museum traces Wales's journey from rural tradition to industrial powerhouse, from the recreated Celtic village to the 21st century Home for the Future. Over 40 buildings have been transported to the museum, stone-by-stone, from all over Wales. Free admission.
Slightly further afield:
If you want to experience our industrial heritage at first hand, warts and all, the valleys north of Cardiff are worth a visit. The valleys were created to house the miners whose coal powered the Industrial Revolution. Once one-third of the world's coal was produced here - it was the Kuwait of its day.
The valleys certainly aren't aesthetically beautiful in the traditional sense, and some areas are terribly deprived, but it is that untouched grittiness which creates the appeal. From the extraordinary Rhondda Valley in the west to Blaenavon in the east you will encounter a post-industrial environment unique in Britain.If you want to go down a real coal mine you'll have to go to Big Pit mining museum in the World Heritage Site of Blaenavon. This is no theme park - this is a real colliery which produced coal for 200 years. Kitted-out in helmet and cap-lamp, you descend in the lift for 300 metres to the real coalface with an ex-miner as your guide.
Merthyr Tydfil (Irontown):
The Heads of the Valleys road (the A465) connects the north end of the valleys. The road passes through the unofficial 'capital of the valleys', Merthyr Tydfil. Merthyr played a vital role in Britain's industrial past: once it had the world's largest ironworks at Dowlais (very little remains), and Richard Trevithick created the world's first locomotive railway (all that's left is a tunnel, but there were centenary celebrations in 2004). The destruction of its industries has left Merthyr a depressed town with little to show of its former glory, the exception being Cyfarthfa Castle, another impressive 19th century castle with excellent museum set in pleasant parkland. The castle was built by the steel magnate William Crawshay who lived in luxury while his workers suffered. From here take the short trip to the Brecon Beacons an area of outstanding natural beauty, you may even decide to climb Penyfan, the highest point in Britain South of Snowdon and less than one hour drive away.