I've loved this castle since I was little girl, it's the ultimate fairy tale castle in Wales. 

 Castell Coch, or the ‘Red Castle’ sits within Fforest Fawr above Tongwynlais.  The first castle on the site was built by the Normans after conquering Cardiff in 1081. It was abandoned shortly afterwards and then reused by Gilbert de Clare to control his freshly annexed Welsh lands. This castle was likely destroyed in the Welsh rebellion of 1314.  

The Castle that stands there today was rebuilt in 1881 by William  Burges (although he died before it was completed) for  the 3rd Marquess of Bute  "as a country residence for occasional occupation in the summer". There was even a vineyard just below the Castle until WWI. 

Find out more info about the castle here.