From the Mixed-up Files of Mrs. Basil E. Frankweiler by E. L. Konigsburg

From the back of the book:
Twelve-year-old Claudia Kincaid is restless. She wants to do something different, leaving her comfortable suburban life in Connecticut behind for awhile. And she wants to be gone just long enough o teach her parents to appreciate her. But as Claudia plans to run away, not just any place ill do. She wants to live in style - in a place with a bit of luxury and some good company. Claudia settles on New York City's Metropolitan Museum of Art. She invites her younger brother Jamie to come along too, not for companionship, but mostly because he is a miser and has saved up some money. Unfortunately, the live-in at the museum isn't all Claudia had hoped. She doesn't feel any different than before. And soon she finds herself in the middle of an interesting museum mystery. Claudia sees a statue so beautiful that she cannot head back to Connecticut until she discovers its maker. the first clue is the statue's former owner, Mrs. Basil E. Frankweiler, an unusual old woman who helps Claudia finally find her way home.