The document discusses castles in Great Britain. It covers castles in Scotland, Wales, London, and Northern Ireland. In Scotland, there are approximately 3,000 castles, many of which are very old with interesting histories. Wales is sometimes called the "castle capital of the world" with over 100 castles still standing. London is famous for castles though many no longer remain intact. Castles in Northern Ireland are marked by the region's tormented history. The author chose this topic to learn about British culture and history and now wants to visit these castles in person.