Formal term for a mosque; モスク is more common in everyday speech.
We visited a mosque in Istanbul.
モスク is the common everyday word for mosque; 回教寺院 is a more formal, descriptive term.
Compound of 回教 (かいきょう, 'Islam', literally 'circling teaching') and 寺院 (じいん, 'temple'). 回教 is an older term for Islam, now often replaced by イスラム教.