城堡 

Pinyin:  chéng bǎo 
Meaning：Castle
Sentence:  城堡的墙很厚。The castle walls are very thick.

More: 

城： 

Pinyin: chéng 
Meaning: Town; city
Radical: 土
Stokes: 9
Traditional: 城
Common words/Phrase:
城市 [chéng shì] 【city】
城区 [chéng qū] 【city district】
城堡 [chéng bǎo] 【castle】
城镇 [chéng zhèn] 【town】
城府 [chéng fǔ] 【shrewdness】

堡： 

Pinyin: bǎo, pǔ, bǔ, pù
Meaning: Castle; position of defense
Radical: 土
Stokes: 12
Traditional: 堡
Common words/Phrase:
堡垒[bǎo lěi] 【fort】 
碉堡[diāo bǎo] 【blockhouse; pillbox】
堡子[bǔ zi] 【fort; fortress】