Where did Claudia and Jamie hide their things?

Claudia and Jamie hid their things in a storage unit at the Metropolitan Museum of Art in E.L. Konigsburg's novel "From the Mixed-Up Files of Mrs. Basil E. Frankweiler." They chose the museum because they wanted to run away from home and live there secretly, using their resourcefulness to survive. Their hiding spot allowed them to explore the museum and learn about art while keeping their presence hidden from the museum staff.