reference room; document room
A room where reference materials, documents, or archives are kept and can be consulted, such as in a library, office, or museum.
I looked up old newspapers in the library's reference room.
閲覧室 is a reading room for general use, whereas 資料室 specifically houses reference materials and may have more restricted access.
Compound of 資料 (しりょう, 'materials, documents') and 室 (しつ, 'room').