。
The east exhibition wing of the museum was closed for cleaning.
Literal
Museum [genitive-の] east [genitive-の] exhibition-wing [topic-は] cleaning [for-のため] closed [progressive-passive-されていた].
Institutional-signage register. ~のため ('for the purpose/reason of') marks the cause. 閉鎖する ('to close off, shut down') is a formal verb, used for facilities, roads, or organizations (not for everyday 'closing a door,' which is 閉める). 陳列棟 ('exhibition building/wing') is a compound formed from 陳列 ('display') + 棟 ('building, wing'). ~されていた is passive past progressive.