The Castle is called Beaumaris Castle. I have added a web site that is official and has photos and stories of it. See related link below. Very pretty place.
Beaumaris
Castle Ditch, Caernarfon LL55 2AYCaernarfon is a North Welsh town on the Menai Straits opposite the island of Anglesey.
anglesey
Situated at Castle Ditch, Caernarfon LL55 2AY Caernarfon is a North Wales town on the Menai Straits
Anglesey is an island situated off the North West coast of Wales next to Gwynedd. It is the largest island in the UK. It is connected to mainland Wales by two bridges - the Menai Suspension Bridge (designed by Thomas Telford in 1825) - the Brittania Bridge (designed by Robert Stephenson)
Wales.
Ynys Mon is the Isle of Anglesey, more commonly known as Anglesey.
Ynys Môn (Anglesey)
Beaumaris Castle was built in North Wales to control the Menai Straights between the Welsh mainland and the Isle of Anglesey.
The island is Anglesey (or Ynys Mônin in Welsh).
There are no cities on the island of Anglesey. Its two largest towns are Llangefni and Holyhead. There is only one city in North Wales, which is Bangor.
ANGLESEY or YNYS MÔN (in the Welsh language)
Anglesey in English; Ynys Mon in Welsh.