Cardiff Castle sits at the heart of the city, a layered history made physical: Roman fort, Norman keep and Victorian Gothic fantasy all on the same footprint. The Roman walls are still visible around the perimeter, dating to around 55 AD when this was a garrison protecting the crossing of the River Taff. The square Norman keep in the centre of the grounds was raised in the 11th century and offers views across the city from its top.
The Victorian Clock Tower and the series of lavishly decorated apartments behind it are the real draw — the work of architect William Burges commissioned by the third Marquess of Bute from the 1860s onward. The Arab Room, the Banqueting Hall and the Winter Smoking Room are among the most extraordinary interiors in Wales: every inch is gilded, painted or carved with medieval and Islamic motifs. The transformation cost an enormous fortune and took decades to complete, and it shows.
Inside the walls, the Firing Line museum covers the history of the Welsh soldier from the 17th century to the present day. The castle grounds are free to enter; the apartments and keep require tickets. Tours run regularly and are worth taking for the additional context.