All over the northern suburbs, there are hidden treasures. Thousands of them are in parks, parking lots and even private yards. They are called geocaches, and they are put there by cachers.

Greg Bergman, of Richland, and his family are avid cachers. "We do it to get out of the house and to do something together as a family," he said.

Mr. Bergman, 44, caches with his fiancee, Christy Noll, 35, and his 14-year-old son, Cody.

Geocaching (pronounced geo-cashing) is a sport in which participants use hand-held global positioning systems, or GPS units, to find geocaches, which are containers filled with treasures. Typically, the treasures are small trading objects such as key chains, toys or pins. The caches also can contain travel bugs or geocoins, both of which are trackable items that can be moved from cache to cache, with their progress traceable online. Some of the items have traveled all over the world, while others are meant to be carried elsewhere, such as baseball fields or amusement parks.

Each cache also contains a logbook, where finders log in the dates of their finds and their names. They then return the caches to their original hiding places, putting the geocoins or travel bugs into another cache.

"We were visiting our friends in Erie over the Fourth of July and they said, 'How would you like to try this new thing we found out about -- geocaching?' We had never heard of it, but we thought, 'Why not?' " Mr. Bergman said.

At first, Cody was less than enthusiastic but, like his dad, he soon became hooked. "Like any teen, he was like, 'This sounds really lame.' But then we went out and we found 15 caches in two days," Mr. Bergman said.

"I like the challenge of finding them," Cody said. "My favorites are the micro-caches."

Micro-caches are small containers that often hold just logs. Caches can be various sizes. Some are puzzle caches, in which cachers use information found at cache sites to solve puzzles. Others are multi-caches, containing more than one site with clues leading to another.

The hand-held GPS systems cost about $75. To find a cache, participants log into the geocaching Web site, www.geocaching.com, and enter their home global positioning coordinates or even their ZIP codes. A list of caches hidden in the area is displayed. Cachers then enter the individual cache coordinates and follow the GPS directions. The caches usually are hidden under logs and rocks or in tree trunks, stuck to guard rails or other spots.

The sport is fairly new. In 2000, government restrictions were lifted that had prevented nonmilitary personnel from using global positioning system technology. That opened the door for all sorts of uses, including the increasingly popular global positioning units in cars.

Just a few days after the restrictions were lifted, David Ulmer thought it would be cool to hide a cache in Oregon. In less than a day, Mike Teague found it. He then created a Web site, and others joined the hunts. Today, there area more than 690,000 geocaches and hundreds of thousands of cachers. More than 30 caches are in North Park, and more than a dozen are in Hartwood Acres.

In the few months they have been caching, the Bergmans have found more than 250 caches and hidden more than 60 in the northern suburbs. "Our record is 51 finds in 12 hours," Mr. Bergman said.

Jerry Angelo, 63, of Hampton, has been caching for more than five years and has more than 630 finds. "I started with my son-in-law. He asked me if I wanted to go caching with him, and I had no idea what it was. After about three finds, I was hooked on it," Mr. Angelo said.

He likes caching "to get out of the house and get exercise." Unlike Mr. Bergman, who likes the "park and grabs" -- quick finds in places that have easy access -- Mr. Angelo likes the long hikes. "I love the scenery that we have been able to see and some of the places we have discovered."

All cachers choose nicknames to use on the Web site and to record logs of finds. Often, the names pertain to other hobbies, physical attributes or places they live. Mr. Bergman's family caches under the name of "Bergie Bunch," while Mr. Angelo uses the name "Frank Drebin," referring to a character in the "Police Squad" and "Naked Gun" movies played by the actor Leslie Nielsen, a man Mr. Angelo resembles.

Amy Seck, of Shaler, caches with her two children, Brayden, 4, and Kyler, 2.

"Since Brayden was always hunting with me, I just created her own account and her name is Bradycakes. It is a name one of our friends always called her," she said.

Like the Bergmans and Mr. Angelo, the Secks use the sport for exercise and fun. "It is something that we can do and have fun as a family," she said. "Brayden loves the adventure of finding a cache, and I love watching the hunt."

The Secks placed a geocache in their front yard but it was "muggled," the term for a cache that has been discovered and damaged by noncachers. "We were disappointed, but we may make another one," Mrs. Seck said.

Mrs. Seck often hunts with her friend, Angel LeGros, and Mrs. Le Gros' son, Jacob, 4. Mrs. LeGros, of Hampton, has one cache in her yard, and the two women have decided to place a holiday cache there. "We are going to name the cache 'It's a Major Award,' " referring to a story line in the family's favorite holiday movie, 'A Christmas Story.' " .

Many enthusiasts cache while traveling or on vacation.

"We are going to my sister's down in the D.C. area and we have a bunch of caches lined up," Mr. Bergman said. "It always adds fun to a trip."