Well-traveled suitcases. Scraped-up ice skates. Old family photographs. Boxes filled with Christmas decorations. These are the kinds of things that many families have tucked away in an attic. You also probably know that sometimes these secret stashes are fun to root around in to see what treasures you might find.

Well, it turns out, the Smithsonian has a secret stash, too - only it has more than a hundred million items in it!

The Smithsonian Institution, which was founded more than 150 years ago as an organization to expand and spread knowledge, is often called the nation's attic. Its museums and research centers have been collecting, displaying, restoring, protecting and studying items from all over the world for generations.

The result is that the Smithsonian's collection has ballooned to 137 million artifacts, works of art and scientific specimens. No matter how you organize it, that's a lot of stuff!

The Smithsonian has so much stuff now, in fact, that less than 2 percent of its collection is on display at any given time. The rest of it usually goes unseen and unknown to the public, a shame, because many of the things in the attic of the nation's attic are just as cool as the things you'd find in any glass case.

KidsPost has chosen a few of these amazing "secret" finds to highlight here. If you want to see more, ask your folks if you can go to www.newsdesk.si.edu and click on "Smithsonian Snapshot." There, the Smithsonian posts each week the story of a fascinating, historic or amazing item. Most of these treasures are not on public view.

"It's just those cool, untold stories that are in our collection," said Jessica Porter, who is one of the employees running the project. "People love the behind-the-scenes stories."

- Margaret Webb Pressler

1 Hope Diamond mail wrapper, postmarked Nov. 8, 1958: The Hope Diamond, a 45-carat blue diamond that is one of the world's most famous gems, is one of the Smithsonian's most popular items. But the valuable gem wasn't delivered to the museum under guard; instead, when jeweler Harry Winston donated it, he sent it in this envelope by regular first-class mail. Winston paid $2.44 for postage, but he insured the diamond for $1 million. That cost an extra $142.85! The original envelope is not on display, but a reproduction can be seen at the Smithsonian's National Postal Museum.

2 "Rudolph the Red-Nosed Reindeer" book, 1939: Today, kids know the famous Rudolph through the Christmas song and TV special. But the character was actually dreamed up by Robert L. May, who was an advertising writer for the now-closed department store chain Montgomery Ward. The Rudolph story was made as a coloring book to give away to kids; 2.4 million copies were distributed. May's brother-in-law, the songwriter Johnny Marks, wrote the song that ensured Rudolph would go down in his-to-ry.

3 Soapman, 1800s: Have you ever heard of an accidental mummy? Workers digging the foundation for a train station in Philadelphia in 1875, possibly on the site of an old cemetery, found this body, believed to be from about 1800, oddly preserved. It turned out that water and soil had seeped into the casket. But the soil had special mineral qualities that created a strange chemical reaction, turning the fat in the body into soap. Don't plan on using soapman to scrub your hands, though: The mummy is stored for research in the Museum of Natural History's dry environment room.

4 Snowflake study, 1890: It's hard to take a perfect picture of a snowflake even today, but 120 years ago it was unheard of until Wilson A. Bentley did it. Bentley became the first person to photograph a single snowflake, by attaching a huge bellows camera (the old-fashioned kind that has an accordion-like back) to a microscope. In 1903, he sent his first 500 pictures to the Smithsonian, which now keeps them in its archives. Bentley's 1931 book of snowflake pictures helped prove the theory that no two snowflakes are alike.

5 Inuit parka, around 1925: To stay warm in the harsh Arctic climate, Inuit cultures have long used layers of clothing made from animal skins, topped with a warm parka of animal skin and fur. Mothers of new babies also wore special inner parkas, called tuillis, which had a pouch to hold the newborn on the mother's back. This ornate version, on display at the Smithsonian's National Museum of the American Indian in New York, is decorated with almost 160,000 colorful glass beads, which became available when the Inuit began trading with European explorers and settlers in the 1800s.

6 Wooden door knocker, late 1800s: Before there were mail slots or mailboxes, how was mail delivered? Letter carriers used to have to knock on every door and hand over the mail in person. But that was hard on the knuckles, so they carried these handy knockers to pound on doors, pain-free. This well-worn item is on display at the National Postal Museum.

7 Fossilized dung of the giant ground sloth: You can see the skeleton of the giant ground sloth, which stood 20 feet tall and lived during the Pleistocene epoch, at the Smithsonian's Museum of Natural History. But you won't be able to see the animal's fossilized poop; it is not on display. It may be gross, but it's important: It was by studying these specimens that scientists determined that the giant sloth, with its foot-long claws, ate leaves, bark and twigs. And by the way, the scientific term for fossilized dung is coprolite.