The indelible memory was forged when the wolves howled back.

The moment came as part of a trip Beverly Rogers was taking with her 10-year-old grandson, Sterling. The pair had traveled from their home in Virginia to the International Wolf Center in Ely, Minn. During their six-day vacation, offered through the adventure travel nonprofit Road Scholar, they had observed nesting bald eagles, hiked to a beaver pond and learned about radio collars tracking the wolf population.

Then, on a starlit summer night, they hiked into the Superior National Forest with a guide who threw back his head back and mimicked the baying call of the wolves.

From deep in the woods, the pack responded in kind.

"This was rare and special," said Rogers, 77, a retired civilian employee of the Army. "It was great to watch your grandchild be exposed to this kind of experience."

More grandparents and grandchildren are discovering the joys of being on the road together. Intergenerational trips, known as "grandtravel" in the industry, are experiencing a sharp increase, with resorts offering special packages, travel agencies booking trips, church camps designating grandparent-grandchild weeks, and some grandparents taking a do-it-yourself approach.

The trend is driven by baby boomers who are redefining grandparenting, said Rebecca Kolls, senior analyst for consumer advisory firm CEB Iconoculture, now part of Gartner.

"They want to instill their values into the next generation; they want to live their legacy, not just leave their estate to their kids and grandkids," said Kolls. "What better way to do that than with time away together? And many of them can afford these vacations."

Road Scholar began in the 1970s as Elder Hostel and set up tours for older adults. It added grandparent-grandchild trips in 1985, and that sector has expanded every year since.

Today, grandparents who are physically and financially fit can choose from more than a hundred domestic Road Scholar trips, which include meals, lodging and hands-on, kid-friendly educational events in packages that start at $449 and reach $2,899. There's particular demand for even spendier foreign travel, with grandparents and grandchildren going on safaris in Africa, taking photo tours of Costa Rica or floating down an Italian river together. Foreign tours for adults range from $2,379 to $6,659, with the child rate starting at $1,899. (Airfare is not included in the rates.)

These trips cut out the middle generation, strictly prohibiting the parents of the children from joining.

"It changes the dynamic when the parents aren't there. That's the secret sauce that fosters the incredible bonding," said JoAnn Bell, senior vice president of program development at Road Scholar. "Grandchildren behave differently when their moms and dads aren't around."

Rogers relishes that. She's taken Sterling's older sister snorkeling in Hawaii, hot air ballooning in Utah and to film school in California. This summer she and Sterling, now 12, plan a Road Scholar trip to Mount Rushmore.

"The trips keep me young and keep me close to my grandkids," Rogers said.

Great DIY expectations

Katie Flannery and Lil Heiland, partners for 28 years and spouses for four, take a DIY approach to vacations with grandchildren.

"I think like a manager and I love to plan, so we put together a pretty tight agenda," said Heiland, 73, a retired clinical director of a mental health center.

Flannery's grandchildren have grown up with the Minneapolis couple; so have Heiland's great-nieces, who regard the pair as bonus grandparents.

A few years ago Flannery and Heiland spontaneously invited the oldest grandson to join them on an excursion to Alaska.

"We usually see them when the whole gang of siblings, cousins and parents get together, and this was such a different experience," said Flannery, 75, a retired social worker. "We created a new connection; everything happens between the three of you. It was such fun to kid him and have him kid us back. We had a ball."

With that, a tradition was born. Since then, Heiland and Flannery have taken two grandsons on a joint camping trip to the Smoky Mountains, complete with biking, rock climbing and spelunking, and made two separate trips to Washington, D.C., with two other grandsons.

"It was fantastic having all that time with just me and them. It's amazing how well your grandparents know you. When they're structuring these scenarios, they think of what you'll like," said Ethan Williams, 16, whose love of history led him to choose the nation's capital for his trip four years ago.

The Rockford sophomore can't pinpoint one favorite memory of the week, but highlights included piloting a flight simulator at the Air and Space Museum that pitched and rolled so realistically that it left his Grammy queasy, laughing as a downpour drenched the trio while they waited to tour the White House and dining on authentic cuisine at a Chinese restaurant.

In the weeks leading up to the trip, the grandmothers assigned Williams a job: manage and coordinate their transportation on the Metro.

"Ethan was in charge — he had to show his independence and figure it out," said his mother, Lucia Williams, 43. "On a family vacation, the parent does it all and the kids come along for the ride. The grandparents had different expectations and that teaches the kid responsibility in a way they're not on the hook for when it's me."

Everyone wins

Grandtravel vacations create a win-win-win situation for three generations.

"Parents can relax because the kids are with people they can count on. Grandparents like to make a difference and feel appreciated and, of course, many are irrationally crazy about their grandkids," said Phyllis Moen, who studies family relationships and holds the McKnight Endowed Presidential Chair in Sociology at the University of Minnesota.

"And for children, the more people they have in their corner, the better," Moen said.

This summer, Heiland's great-niece Sadie will travel to Guatemala with her Aunt Lil on a trip sponsored by the 11-year-old's Spanish immersion school.

Sadie bubbles with excitement about their plans to use their Spanish, tour Mayan ruins, volunteer at a community school and ride a zipline together.

"Lil is honestly so peppy that I'll be the one telling her it's time to take a break," Sadie predicted.

Flannery and Heiland prefer to take the next generation on their special trips when they're between 11 and 13; they consider that the ideal age for them to be mature enough to be away from home, keep up with the itinerary and engage in the planning.

"We have a tremendous enthusiasm for introducing kids to things they wouldn't otherwise do," said Flannery. "I compare this with what I did with my grandparents, which was mostly sitting. What we do is exhilarating."

With two granddaughters and a great-niece who aren't yet old enough to be their traveling companions, Flannery and Heiland have additional trips to anticipate.

"Something deepens between us after we share this time. We know each other in a different way that will always be part of our relationship," added Heiland. "That's the part I like best."

Ethan Williams thinks his vacation with Flannery and Heiland reframed their bond in a lasting way.

"I'm absolutely closer to them. They are very fun people," he said.

"Everyone should do this with their grandparents. It should be a tradition in every family."

Kevyn Burger is a Minneapolis-based freelance broadcaster and writer.