Geocaching, a technology-driven treasure hunt, is gaining popularity worldwide. As of Aug. 3, there were 188,437 active treasure sites (caches) in 216 countries. The number of sites grows by the hundreds daily.

Caches can be found in such faraway places as Kabul, Afghanistan; Moscow, Russia, even Antarctica. And they are as close as neighborhood parks here in Cupertino.

In fact, Cupertino could be called a "cache cow," as there are over 6,000 active caches.

Geocaching (pronounced "geo-cashing") is not about the treasure, says one local geocacher. It's about the hunt.

"You just never know what you're looking for until you find it," says Betsy Fessler, a Sunnyvale business owner. "It makes you go to places in your own backyard that you've never been to."

Geocachers carry on their search with the help of www.geocaching.com and a GPS unit, which costs around $100. Coordinates for every registered cache are listed on the website and can be downloaded to GPS units. These handheld devices give directions to a specific destination.

GPS (global positioning systems) send signals through satellites and receiving devices to compute positions, or coordinates, on the Earth. Fessler says her GPS unit can get her within 20 feet of the coordinates. After that, she says, it's about instinct, determination and a little bit of luck.

The Q & A section at www.geocaching.com says "[Geocaching is] deceptively easy. It's one thing to see where an item is; it's a totally different story to actually get there." The website is recognized as the official site of geocaching worldwide.

Getting there can be difficult sometimes, Fessler says. That's why the website offers treasure hunters two ratings--one on how hard the cache is to find and one on how difficult the terrain is. Both ratings give a 1-to-5 scale, with 5 being the most difficult.

There are also hints, but they're not supposed to be explicit enough to be what geocachers call "spoilers."

Some of the more obvious caches are found upwards of 100 times, Fessler says, while the difficult ones in rural areas are seldom found. Fessler says she and her family placed a cache at the top of the Steam Shovel Trail in northern Nevada, a spot only accessible by four-wheel-drive vehicles.

"[Geocaching] seems so conducive to offroading," she says.

Four-wheeling is one of her family's biggest hobbies, Fessler says, so the family's username on the website is the Buggy Bunch.

Geocaching on vacation is lots of fun, she says, but she also enjoys hunting for treasure near home.

One warm July day, Fessler downloads coordinates of four caches into her GPS unit and hits the road to Sunnyvale Baylands Park.

The first cache, called "Baylands Cache & Carry," is located at coordinates N 37deg 24.811 W 122 deg 00.047. Account holder WeBeDnD, who placed the cache, mentions in the hint column that there will be a pine branch pointing to an ammo box that contains the cache. The hint helps, but it doesn't give the location away.

"It's designed so that if you are looking for it, you can find it. If you're not looking for it, you won't stumble upon it," Fessler says.

It turns out, the ammo box is buried in a pile of pine needles. The treasures are small and silly, including 20th century cassette tapes from such musicians as Loverboy and Amy Grant. There's a picture of three-month-old Joy. The back of the picture doesn't give any more information about the baby. There's also a pen and a pencil, a 2006 calendar and an action figure among the items.

Aside from treasures, there's a log in most caches where geocachers can write their username, the date they found the cache and what they left and took from the cache, if anything.

Some geocachers don't trade treasures, preferring just to find the cache and sign the log. Fessler says she is most interested in signing the logbook so she can get credit on the website for her "find."

Fessler replaces a necklace and Sade cassette tape with some of her children's toys, including a miniature skateboard. She says the children's trinkets make great treasures.

"My kids are a plentiful source of all sorts of junk," she says, heading off to find the next cache.

The GPS says the second cache, called "Baylands Grove," is 346 feet from the first one to the north-northwest. This one will be harder to find; it got 2 1/2 stars in difficulty. It's a micro-cache, also called an urban cache, Fessler explains. Urban caches are smaller and blend in with urban surroundings such as concrete and metal.

"Micros can defeat you easily," she says. "They're pretty hard."

According to the GPS unit, Fessler is close. The hint says the cache is "not visible from most any angle if replaced correctly," and it turns out to be true. Fessler squats down, reaches into the base of a metal tower and pulls out a film canister with a magnet secured to the side.

People walking by ogle Fessler. She says geocachers call oglers "muggles."

Before searching for the last two caches, Fessler takes care of some environmental responsibilities--picking up litter around the area. The acronym CITO on geocaching.com stands for "cache in, trash out," and it asks all geocachers to pick up trash and limit their impact on the natural environment.

"The unwritten rule is that those hiding caches don't promote the tromping of natural environments," Cupertino resident Steve Bernstein says.

Bernstein says his love for hiking led him to geocaching. He used to design trail maps that could be downloaded to GPS units for geocachers who were also interested in hiking.

"Geocaching is a great way to get kids interested in hiking," he says. "It makes it fun for them."

Back at Baylands, Fessler searches for the last two caches. The third, called "Aw Nuts," is more difficult and has her trudging along a trail that parallels Highway 237. She eventually makes it to the base of a walnut tree where the cache is a plastic peanut butter jar, painted dark green. The fourth cache turns up easily on the way back to her car.

According to geocaching.com, this high-tech hunting began in 2000 when President Clinton signed an order that made Global Positioning Systems available to the public. After that, a man hid a container of goodies near Portland, Ore. The first man to find it, Mike Teague, built a personal webpage to document his find. Later that year, Jeremy Irish approached Teague about developing a new website and the activity was named geocaching. The website has since taken on a life of its own.

And so has geocaching, with some variations.

For instance, there are travel bugs in some caches. These items are registered on the website and picked up by cachers and carried to new sites. The item becomes a "hitchhiker" carried from cache to cache, in some cases around the world. Each bug has an online diary, and geocachers sometimes submit pictures of the bug's travels.

Some bugs actually have missions.

Fessler says her brother wanted his travel bug to visit as many racetracks as possible on the NASCAR circuit. His bug made it to Daytona Raceway in Florida for the Pepsi 400, and its picture was taken on the dashboard of a truck that drove on the track.

Geocaching can be done on many levels, Fessler says. Anyone can do it, from novices to weekenders to hardcore cachers. But, Fessler warns, don't expect caches to be easy finds.

"People are getting pretty creative with this stuff these days."

For more information on geocaching, visit www.geocaching.com. Registration is free.