> Town or region: Prague, Czechia
> Century: 9th
The Guinness Book of World Records identifies this edifice — an irregular polygon covering a total surface area of 18 acres — as “the largest ancient castle in the world.” Today it serves as the office of Czechia’s president.
Château de Chillon
> Town or region: Chillon (Lake Geneva), Switzerland
> Century: 10th (?)
This island redoubt, built on the site of a Roman garrison and long occupied by the Counts of Savoy, is one of the most often visited castles in Europe.
> Town or region: Alnwick, England
> Century: 11th
The UK’s second-largest inhabited castle, dating from Norman times, has not only been home to the Percy family for more than seven centuries but has also served as a teaching college, a military base, and a film set — starring as Harry Potter’s Hogwarts School..
> Town or region: Vianden, Luxembourg
> Century: 11th-14th
A Renaissance manse was added to this massive castle west of the Rhine in the 17th century. The whole place later fell into disrepair, but has recently been restored.
> Town or region: Windsor, England
> Century: 11th-19th
No other castle in Europe has been continuously occupied for as long as this seat of the British monarchy. Frequently depicted in paintings and photographs, it is one of the world’s most recognizable castles.