“So, you go out in the woods and get a Tupperware full of junk?”

That, Kurt Milligan recalled, was his initial reaction to geocaching.

A lot has changed since then.

Today, Milligan and his longtime friend-business partner EJ Martin own two geocaching websites — madcacher.com and navicache.com — and recently published “101 Devil Caches,” a book about geocaching. It’s safe to say that both men, fellow 1999 graduates of Mountain Valley High School in Rumford have caught the geocaching bug.

“I think what appeals to me is that I’m a big outdoorsy guy anyway, so it just gives me another reason to go out,” Martin said. “If I’m going to go snowshoeing in the middle of the winter for three hours, that’s enjoyable in itself, but if you have some goal along the way of finding a geocache, that’s even better.”

If you haven’t read up on this relatively new sport, geocaching is essentially a modern day, worldwide treasure hunt that combines technology with outdoor activity. With a GPS in hand, geocachers travel to specific coordinates to find caches — watertight vessels that contain a log book and a variety of small “treasures.”

Unlike a pirate on the high seas, a geocacher doesn’t take all the treasure and run. Instead, the geocacher trades — he brings his own “treasure” (a tin soldier, jewelry, a keychain) to add to the cache, then takes a trinket of equal value.

At least, that’s traditional geocaching. It has branched out from there.

You can walk people to death

Geocaching has evolved rapidly since it first became popular in 2000, when the website geocaching.com was launched by Jeremy Irish, former member of the U.S. Air Force and owner of Groundspeak, a company with the mission “to inspire outdoor play using location-based technology.”

In today’s world, many are concerned with the amount of time people — especially children — spend indoors, in front of a computer or television. And organizations such as the No Child Left Inside Coalition are working to reverse the trend of “nature-deficit disorder,” a term coined by author Richard Louv in 2005 to describe “psychological, physical and cognitive costs of human alienation from nature.”

Geocaching is just one way to trick people into going outside. You start sitting in front of the computer, but sooner or later, you have to walk out the door to find the treasure.

“I have a really good time going outside and going hunting and stuff like that, and I think people are really missing the being outside aspect of life,” Milligan said. “You have to get outside and actually live a little bit.”

Encouraged by his father Gary, Milligan tried geocaching for the first time while vacationing at his family’s timeshare in Las Vegas. He wasn’t excited about it — until he found his first cache. Then, he wanted to find the next closest cache. And after he found that, he started searching for the next.

“I ended up walking about six miles finding caches that day,” Milligan said. “And I thought, ‘Wow. I got a lot of exercise.’”

Some people enjoy seeking multi-caches, geocaches that require seekers to visit multiple locations before finding the final cache. Often, each location provides clues to the next location.

“You’ll get on a string of them, and you’ll keep trying to find that next cache,” Milligan said. “You can walk people to death if you space them out right.”

A year-round activity, geocaching can involve hiking or snowshoeing, swimming or ice skating, skiing or biking, snowmobiling or four-wheeling — you get the idea.

“We want to plan community events and push to get kids away from the computer and outside a little bit,” Milligan said. “With geocaching, you have the technology stuff — still going online and all that — and you have the outdoor exercise.”

Places you didn’t know existed

Martin, who currently lives in Gray, has moved a few times over the years. And when he moved to western New York, he used geocaching to get his bearings in the new town.

“I think I spent 3-4 weekends geocaching, and by the end of that, I knew where I was and even ran into some really great restaurants,” he said. “It’s a great way to get to know an area.”

Martin’s favorite aspect of geocaching is that the activity serves as a conduit for exploration, whether it’s in a metropolitan area or the forest.

“You find a lot of trails and places that you didn’t know existed,” Milligan said. “People can hide geocaches in really cool places — a waterfall you normally wouldn’t hike to or some sort of geological feature. Finding those places with friends and family helps build relationships.”

If you’re wondering who’s hiding all the caches, the answer is: everyone and anyone. Geocachers can construct and hide a new cache any time, but they have to follow a few guidelines, which are listed in detail on any website that lists caches.

Most of the guidelines are common sense. For example, you have to ask before you hide a cache on any land that you don’t own. But then there are a few rules that may come as a surprise, such as “caches are never buried, neither partially or completely” and “physical elements of different geocaches should be at least 0.1 mile apart.”

“It has been an issue in some places where people will hide an ill-designed cache in an urban environment, and bomb squads come out,” Martin said. “I think it just comes down to common sense.”

After hiding a new cache, you post the coordinates online on a geocaching website such as geocaching.com, navicache.com and terracaching.com. But if you hide a cache that breaks a rule, odds are, your fellow geocachers will remove it.

You’re always sharing something

As geocaching evolved, it gave birth to travel bugs and geocoins — treasures that can be tracked as they move from cache to cache. Each bug and coin sports an identification number, which can be looked up on geocaching.com, where you’ll learn where it originated and where it has traveled.

Some bugs and coins have special missions, assigned by their creators. For example, some have missions to reach certain places.

And some bugs and coins have special tasks. Anyone who takes it from the cache must conduct the task before passing it to the next person or placing it in another cache. For example, one geocacher created a “sticky bug,” a travel bug attached to a small book, and each carrier had the task of adding a sticker to it. Often, tasks require the carrier to post a photo on the coin or bug’s tracking page on geocaching.com.

“I personally really enjoy the travel bugs,” Martin said. “I think just reading the stories or the mission that it gets sent on is interesting — looking at the photos and that sort of thing.”

“‘Geocaching] is really community focused,” Milligan said. “That’s one reason I like it. You’re always sharing something online, always encouraged to leave a note or post a picture.”

Good geocaching etiquette means reporting all geocoin and travel bug removals and placements, and not holding onto them for too long. They’re meant to travel, after all.

“It’s fun for families to send out a bug,” Milligan said. “They can get online and might find that it’s in Japan. It’s a lot of fun and just brings people together a little bit more.”

To give you an idea of the scope of the game, there are 2,180,133 active geocaches and more than 6 million geocachers worldwide, according to geocaching.com, which is currently translated into 20 languages.

“I was surprised about how many were in my hometown,” Milligan said. Geocaching.com lists 620 caches — traditional and nontraditional — within 25 miles of Rumford. Elsewhere in Maine, you can find 881 caches within 25 miles of Bangor, and 261 within the same distance of Presque Isle.

While geocachers mostly share their adventures online, they also get together in the real world. This year, the 11th annual Geowoodstock — the largest gathering of geocachers in the world — was held on May 25 in Lakeland, Fla. And in October, Milligan plans to attend Geocoinfest — the largest gathering of geocoin enthusiasts in the US —  this year will be hosted in Las Vegas.

In individual communities, geocaching clubs host smaller gatherings such as Cache In Trash Out events, where people go geocaching and pick up trash along the way.

The Maine Madcachers

“If there is any misconception about geocaching, it’s that it’s all drive up and park — easy to get,” said Milligan. “But there are some [caches] that you have to go scuba diving for, and there’s one on the International Space Station.”

In addition to the traditional geocache, there are now puzzle caches, mystery caches, themed caches (such as The Celtics Cache), reverse caches, virtual caches and more. Caches can be nano size (usually made with DNA tubes) or quite large (a 5-gallon bucket).

And then there are “devil caches,” a term coined by Milligan and Martin in “101 Devil Caches: Your Guide to Creating Unique or Hard to Find Geocaches,” published January 2013.

“I like the challenging ones,” Milligan said. “I figure, if I had to hike that far to find something, I want it to be difficult to find.”

“One cache took me six tries to find,” he continued. “It was a tiny magnet inside of a sign that I just couldn’t see.”

A devil cache is simply a cache that is difficult to find.

In “Devil Caches 101,” the duo provides a brief rundown on geocaching history and terms, then dives into 101 devil caches, including the Christmas ornament cache, chewing gum cache, fake bird cache, hornets nest cache, all presented with diagrams, instructions on how to build them and potential hints to post online with the coordinates.

After reading the book, you may understand why they’re the Maine Madcachers.

Jump in and do it

In the Harry Potter book series by J.K. Rowling, “muggles” are people who don’t possess magical powers. But in the geocaching world, “muggles” are people who don’t know about geocaching. And a geocache can be “muggled,” discovered by a non-geocaching person, who steals it or damages it.

In Harry Potter, muggles are muggles. They can’t be wizards — ever.

But in the geocaching world, muggles can easily become geocachers. All they have to do is read the rules, pick up a GPS and go find a cache. To share your adventures, you can sign up for free at geocaching sites like navicache.com or geocaching.com.

“I would say, just try it. It’s one of those things you have to just jump in and do,” Martin said. “Then share it with others. It’s a great thing to do on a Saturday if you’re sitting around with nothing to do.”

Nowadays, you don’t even need to purchase an expensive handheld GPS, Milligan pointed out. If you have a smartphone, there are several GPS applications on the market (many of them free).

“I would encourage people to find one that they’ve probably walked by every day and never knew was there,” Milligan said. “That usually gets the bug in there.”

Aislinn Sarnacki

Aislinn Sarnacki is a Maine outdoors writer and the author of three Maine hiking guidebooks including “Family Friendly Hikes in Maine.” Find her on Twitter and Facebook @1minhikegirl. You can also...