There are many reasons people don’t incorporate adventure into their lives. It takes time, money, expertise, and equipment to do things like scale the world’s tallest mountains, traverse its deepest canyons, and navigate its many waters.

But it doesn’t have to be that way, says Alastair Humphreys, a travel writer and National Geographic Adventurer of the Year. In 2011, he set out to dispel the myth that an adventure needs to be an epic odyssey. Mr. Humphreys coined the term “microadventure” to spread his philosophy that one doesn’t have to travel far or spend a lot of money – or any money at all – to have a meaningful experience. His classic example of a microadventure is a family sleeping outside in the backyard under a starry summer sky. “Without a tent, there’s a definite feeling of wildness,” says Humphreys, who lives in a village outside London.

The concept took off. A search for #microadventure on Twitter yields multiple posts daily, and on Instagram there are thousands of photos from microadventurers satisfying their wanderlust by climbing trees, canoeing, cycling, trail running, or backpacking.

“Had ... an amazing #microadventure with my buddies last night,” tweeted southdownsmtbskills. The 45-year-old Brit, known as Jim Barrows in the real world, hitched a sleeping bag to the handlebars of his mountain bike and, along with four friends, rode 12 miles to Rackham, England, after work, where they camped for the night.

Microadventures are also making gains in the United States. Boulder, Colo., resident Lauren Rains was so inspired after reading Humphreys’s travel blogs last year that she tried a notable microadventure of her own: She rode her longboard 30 miles from Boulder to Denver.

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Meanwhile, Humphreys spent 2013 engaged in various types of microadventures. His book, “Microadventures,” will be available in June. His favorite experience might not even quite merit the special label, but he counts it among his adventures. “A full moon comes up at the same time as the sun sets, which is a very convenient time for a walk,” Humphreys says. “I walked a few hours from my home to a rural train station, and then took the train back. It was absolutely beautiful.”

Humphreys advocates a unique type of microadventure that he calls an arbitrary journey – similar to what Ms. Rains did longboarding from Boulder to Denver. It’s a journey that matters only to the person taking it. In Humphreys’s case, he spent an afternoon biking from the house his father grew up in to his mother’s childhood home.