Cardiff Castle stands in the middle of the city of Cardiff, just North of the city centre (I’ll use British spelling), quite easy to get to if you’re out on the town, just remember that they close at 6 and stop letting people in at 5. Definitely go see it if you’re traveling in the area.
From what I remember from watching Secrets of Great British Castles, Cardiff Castle stands on the ruins of an old Roman fort, and was originally constructed during the reign of Edward I. Talking with an Englishman at the bar one night, evidently castles of this sort are called “war castles,” built during either the Norman Invasion or the English conquest of Wales under Edward Longshanks. As you can see, it’s a motte-and-bailey style, but of course the original structure would have been made of wood.
Cardiff Castle is sort of looked down upon by locals specifically because it isn’t all original, though I don’t know why, if they were already building it in stone by the 1200s. The main problem is that the Marquesses of Bute started their own “restorations” in the 1800s cashing in on the gothic revival fad of the time (many wealthy noblemen of the time tore down castles built in the 14th and 15th centuries to make something more in keeping with what was considered a castle at the time). I believe there was rather a large stink raised about the demolition of the medieval inner bailey wall along with other buildings dating from at least the 1300s. The grounds of the bailey would have held extensive gardens, but now are just lawn.
There was a rather impressive collection of buildings on the outer bailey wall built (or restored) during the 1800s and containing rather impressive living quarters, said to be kept as close as possible to medieval dwelling conditions. Unfortunately I did not have enough time to take the tour, preferring to wander the castle grounds by myself and only leaving right when they closed. I’m still impressed with what I saw, and coming from a country where something built in the 1850s is considered old, Cardiff Castle is still properly ancient.