The Secret Garden Illustrated: by Frances Hodgson Burnett

When orphaned Mary Lennox moves in with her uncle on the Yorkshire Moors, she discovers a house full of secrets. Her uncle keeps himself locked up in the mansion, which contains about a hundred rooms. And she hears crying along one of the long halls late at night.
Mary's only respite is the vast property's surrounding gardens. Then Mary stumbles onto a hidden garden, which is encircled by walls and locked with a lost key. Mary discovers a way in—and becomes determined to bring the garden back to life—with the help of two unexpected companions.