"No, those castles are not big."
Translation:Ne, ty hrady velké nejsou.
This is what I've found in Wiktionary: The word hrad is used for castles whose main function seems to be defence, while zámek is used for those whose main function seems to be ostentation. For example, the castles of King Edward in Gwynedd are hrady, while the Loire Valley castles are zámky. The difference can be subjective, so that for example Windsor Castle can be called by either term by different speakers.
The words are "zámek" and "hrad".
Hrad is a huge medieval structure on a hill, usually featuring a lot of stone - walls, towers, battlements. Imagine Game of Thrones or L.O.T.R. type of ambiance. Prague was founded around a castle (the Prague Castle - Pražský Hrad).
Zámek is sometimes translated as a manor house or palace. It's typically from a later period than those medieval castles, and it's much more decorated - outside and inside. Imagine dukes and barons and earls, dancing balls and high society and wigs and chandeliers and beautiful furniture.