Tongwynlais is located 5 miles north of Cardiff in South Wales. It is near Junction 32 of the M4 motorway, which runs from London to Carmarthenshire. Surrounding towns and villages include Coryton, Radyr, Taffs Well and LLanishen.
Standing in the village is the striking folly known as Castell Coch, or Red Castle in English. It stands on the former site of a 13th century castle which was built by Gilbert de Clare as a defence against attacks from the Welsh.
One of its most interesting features was its dungeon, which only had light from two very faint rays, which met on the centre of the floor. As legend goes, treasure is buried on the site and two ravens guard it. Sadly no treasure has ever been found in the folly, but no doubt some people are still searching for it.