WHEN I TOLD my son we were going to visit a museum with a book he could climb into, his face clouded over. "Can I come out again, Mommy?" he asked.

As it turns out, David found it easy to slide out of the three-dimensional book exhibit at the Cloisters Children's Museum. I, on the other hand, found it harder to leave. Visiting the unique museum in Brooklandville, Md., was one of those rare experiences I undertook for my son's benefit that probably evoked more of a sense of magic for me than for my two-year-old.

It began with a drive to a wooded area outside Baltimore, seven miles north of the Inner Harbor. The first thing we encountered as we got off the expressway at Brooklandville was a row of 19th-century stone buildings surrounding a gristmill. This was the first sign that we had entered a time warp. Soon afterward we entered the Cloisters estate through a black wrought-iron gate. Waiting for us at the end of a long, wooded driveway at the top of the hill was the whimsical building often referred to as "the castle."

Its architectural style has been called French Tudor Gothic Revival -- "folly" for short. There are two griffins guarding the entrance, human and animal gargoyles looking down from the walls and a leaded-glass door beckoning you in. The Cloisters is the former home of industrialist Sumner Parker and his wife Dudrea, a couple described by museum staff as "creative, charming and very eccentric."

What you notice about the castle inside, first and foremost, is its human scale. This is a children's museum, and it is not institution-sized. There are several large rooms on each floor, but the space is manageable. You never feel lost or overwhelmed. There are also no high-tech science exhibits here; the emphasis is on make-believe play.

"We want children to become part of every exhibit," says Natalie Pilcher, the Cloisters' programs director. "The children can put on costumes and take on a character as they enter each exhibit."

This makes the museum a playground rather than a strictly visual experience, Pilcher says.

The Cloisters is a place for creativity and imagination. There are costumes and musical instruments and doll houses and play houses and lots of wooden blocks. Besides the book you can climb into and slide out of, there is a post office you can mail letters from, a make-believe village you can deliver letters to, a wooden train you can conduct around a track, a barge you can pilot against the backdrop of the Baltimore Harbor and a room full of antique doll houses.

How do you possibly squeeze all this into a small castle? By making everything child-size, compact and integrated. Every one-room exhibit offers a make-believe world complete with costumes, sets and props. Literacy is an important theme at the Cloisters, so every exhibit also includes age-appropriate plaques and reading or writing activities. The postal exhibit, for example, offers a sample letter that can be completed and sent to an imaginary pen pal, a postal weight chart and a real scale, wooden stamps, a sorting bin and a Zip code map of the United States showing where the pen pals live.

Most of the current exhibits are only a few months old, and there is a shiny-new look to them. But fantasy creatures of indeterminate age also share the exhibit space, including a walrus called Waldo the Wise, a fantastical orange "Dragon Bird," and a musical monster whose body parts include a washboard, cymbals, xylophone and a twisted horn.

Tucked under the eaves on the third floor is a cozy reading nook, with books arranged under carpeted risers and an overstuffed lavender wing chair. I could have spent hours there, but David wanted to play with the wooden doll house in the next room.

As he played, I studied the gargoyles carved into the heavy wooden cross-beams. The capricious design of the castle also appeals to adults, and gives them something to think about while children are exploring their own universe. I was intrigued by the winding stone staircase, the diamond-paned windows, the cloistered courtyard that gave the home its name, and the nearby windmill that served as Sumner Parker's studio.

The Cloisters, situated on 53 wooded acres, also encourages children to explore the outdoors. The estate is home to rabbits, deer, porcupines, wild turkeys, quail, owls and many other species of birds. Three marked nature trails range from a quarter of a mile to a mile in length. The museum offers periodic nature walks, visual scavenger hunts and other outdoor activities.

In addition to a "butterfly garden" and a crafts space inside the windmill building, the Cloisters is home to an intimate outdoor amphitheater, where concerts and performances are held on spring and summer weekends. During the winter and on rainy days, these events are moved inside.

With all this bounty, what does my son remember best about our visit to the Cloisters? Playing with a real-live cash register. Next time, I'll drop him off at a supermarket and visit the castle by myself.

Daphne White last wrote for Weekend about hotel and resort programs for kids.