Here are some photos of castles from around the UK (none from Wales unfortunately ). You will be able to find lots of much better photos of these and other castles on the internet. When you are looking at castles always be wary about what you are seeing because they have often been rebuilt or remodelled over the years.
Urquhart Castle Loch Ness
A more colourful Picture of Edinburgh castle
The bishops castle Glasgow which is a modern recreation of the original one
Bedlay castle Chryston a few miles to the east of Glasgow
I think this is Greenan Castle. A great example of how not to take a photo.
On the other side of Scotland not much is left of Dunbar castle
Not much left of Berwick castle either. They built the railway station right were the castle was.
Bamburgh castle. it is right next to the sea and there are lots of amazing photos of it.
This is the smallest castle I have seen. Its Drumburgh castle but its only really a fortified house.
Thirlwall castle Near Hadrians wall and no doubt built using a lot od Roman stones.
Newcastle Keep. Like Berwick they built a railway right through the castle.
Durham Castle. This building was built in the 1840s
The building on the top of the hill is the real Durham castle
Cliffords tower York
Lincoln castle which has two mottes which is very unusual.
Nottingham castle Gate. only the foundations are genuine.
Notting castle from below. This is a 17th century mansion which was built on the site of the castle