noun
Refers to the principal building of a complex, as opposed to an annex (別館), outbuilding, or detached wing. Common in institutional contexts such as museums, libraries, hotels, and hospitals.
博物館の本館は改修中で、別館だけ見学できます。
The museum's main building is under renovation, so only the annex can be visited.
ホテルの本館と新館は地下通路でつながっている。
The hotel's main building and the new wing are connected by an underground passage.
noun
this building (library, museum, theatre, hall)
Used within an institution to refer to the building itself, similar to 'this library' or 'this museum' in English. The specific meaning depends on the type of facility.
本館では、毎週土曜日に映画上映会を行っています。
This building holds a film screening every Saturday.
ご不明な点は本館１階の受付までお尋ねください。
If you have any questions, please ask at the reception desk on the first floor of this building.