Brad Ryan and his 89-year-old old grandmother Joy Ryan have visited 29 national parks so far and have no intention of stopping until they've visited all 61.

The first one they saw, Brad told "Good Morning America," was the Great Smoky Mountains National Park in 2015. Since then, he and Joy Ryan have been to Badlands, Yellowstone, Glacier, Yosemite, Joshua Tree, Grand Canyon, Zion and Mammoth Cave, among others.

"I remembered a prior conversation with my Grandma Joy when discussing my 2009 Appalachian Trail hike from Georgia to Maine, and she expressed regret that she had never seen the mountains and explored the great outdoors throughout her life. So I invited her to join me on my weekend escape to the Smokies," Brad said.

At the time, Brad was a fourth-year veterinary student at The Ohio State University College of Veterinary Medicine.

"I needed an escape from campus during my clinical year after news of a second-year vet student's suicide was made public," he said.

A highlight for Brad was "watching my grandmother tap into her inner child as she rolled down a sand dune at Great Sand Dunes National Park and Preserve at age 87." So was being trapped in an hours-long traffic jam of a bison herd in Yellowstone's Lamar Valley and watching the sunrise over the Grand Canyon.

Some of the memories were less fun than others.

"Being charged by a moose along the shores of Fishercap Lake in Glacier National Park," he said.

The duo hopes to visit the remainder of the parks sometime in 2020 to celebrate Joy Ryan's 90th birthday. They have a GoFundMe which has helped fund their travels.

"We have received a lot of support from around the world so far, and I am hopeful that opportunities will arise to make it feasible to travel with Grandma Joy to the most remote US National Parks," Brad said.