Refers to the space directly under the roof, often used for storage or as an extra room.
Old photos were stored in the attic.
When I was a child, the attic room was my secret base.
床下 refers to the hidden space beneath the floor, while 屋根裏 refers to the hidden space beneath the roof (the attic) — the two opposite ends of a house's structure.
attic; garret; loft
Compound of 屋根 (yane, 'roof') and 裏 (ura, 'back' or 'underside'), literally 'the space behind/under the roof'.