There are about 150,000 of them spread throughout 213 countries and you need satellites to help you find them. What are they? They're geocaches and geocaching is a sport that is quickly gaining popularity.

The geocaches come in all different sizes and shapes. Usually stored in a waterproof container, these caches are treasures of minimal value. The container is often a Tupperware container or ammo box. The "treasures" can be just about anything you can imagine: a mini-stapler; a toy soldier; foreign coins.

How do you find them? That's the satellite part. If you haven't been in a cave for the last five years, you've probably heard of the Global Positioning System, or GPS. Just in case you're one of the cave people, GPS is a system of 24 satellites orbiting the earth at an altitude of 11,000 miles. A small handheld receiver, a little larger than a cell phone, picks up signals from the satellites and can pinpoint your position anywhere on earth, sometimes as accurately as 3 meters.

If you go to Geocaching.com you can enter your location by ZIP Code, state, or country and get a list of caches in your area. Each listing has a log of who found the cache, when it was found, and usually what trinkets were taken and left.

You are given the coordinates of the cache in degrees of longitude and latitude. Enter those numbers in your GPS and start following that little handheld device. It may sound easy, but depending on the individual cache, it can be a challenge.

Some examples of hiding places are in holes at the base of large trees, holes in the face of a cliff, and some are even found in urban areas. One is under a bridge accessible only by rope. Another clever place was created when a cable company worker attached an empty cable connection box to the side of a building.

As you can imagine, public parks are popular places for hiding caches. However, they're not allowed in National Parks in the U.S. Geocachers, being outdoor sort of people, are mostly ecologically--minded, and there is even a "cache in trash out" program that promotes participants picking up trash that they may find while hunting treasure. Many places require permits for placing caches. Park authorities' main concern is damage to sensitive areas such as wetlands or locations of endangered flora or fauna.

GPS receivers start at about $75.00 US and can be purchased at some department stores, sporting goods stores, or ordered online. Amazon.com often has very good prices. Geocaching really is a lot of fun and it's a great way to get outdoors and get some exercise.