"From the Mixed-up Files of Mrs. Basil E. Frankweiler"

by E.L. Konigsburg, YR, 1967, 162p, rating=3.5
Newbery Medal winner 1968

When Claudia decided to run away, she planned very carefully. She would be gone just long enough to teach her parents a lesson in Claudia appreciation. And she would go in comfort-she would live at the Metropolitan Museum of Art. She saved her money, and she invited her brother Jamie to go, mostly because be was a miser and would have money.
Claudia was a good organizer and Jamie had some ideas, too; so the two took up residence at the museum right on schedule. But once the fun of settling in was over, Claudia had two unexpected problems: She felt just the same, and she wanted to feel different; and she found a statue at the Museum so beautiful she could not go home until she had discovered its maker, a question that baffled the experts, too.
The former owner of the statue was Mrs. Basil E. Frankweiler. Without her-well, without her, Claudia might never have found a way to go home. (book cover)

Excellent blurb.  And so the sister-brother team took on the adventurous journey of living in hiding in the Metropolitan Museum of Art.  The 7 day escapade was full of humorous dialogue, compromise, and discovery.  All told from Mrs. Frankweiler's point of view .. the old lady that had the mixed-up files that held the answer to the mysterious Angel statue in the museum ... was it by the one and only Michelangelo?

In the end, Claudia with the help of Mrs. Frankweiler was able to feel different ... not differently, hence, she was able to return home with glee.  She found the heroine in herself.

It would be fun to have the museum all to yourself to learn and play in ... just for a few days.  Any longer, I'd miss my bed too much.   Aahhh, the minds of young kids.