Great thread idea Nuno, well done
If I remember correctly, the UK, former Czechoslovakia (now Czech Republic and Slovakia) and Liechtenstein have the most castles/palaces in total and per square mile (or km, as the case may be), respectively, in the world. Needless to say, having spent the majority of the past several year here, I have seen a few dozen or so of them. Some, such as the famous Prague Castle shown below, are simply stunning. A few of my other personal favourites are Hluboká (Schloss Frauenberg) in south Bohemia, Karltejn (Burg Karlstein) - founded in the 14th Century by Charles IV and Červená Lhota, a beautiful red chateau located on a small rocky island set in the middle of a lake, which is also in south Bohemia.