The straight-line distance from the north to the south rims of the Grand Canyon is about 10 miles.
By road, it's a 51â2-hour, 220-mile drive.
On foot, it's just about a marathon - 25 miles, give or take - with around 10,000 feet of elevation change. In what can be brutal conditions.
No wonder, then, that the rim-to-rim hike has been described as one of the best day hikes in the world. And it's no wonder the National Parks Service discourages trying the rim to rim in a day - or at all, for that matter, by the ill-prepared.
"So many people who choose to do it," said Marc Yeston, a Canyon District Ranger, "don't know what they're up against and end up needing to be rescued. Some even end up dying. If you know what you're getting into and are prepared physically, it can be done safely. But if you're not prepared, it's dangerous."
Nearly three years ago, Lawrence's Pat Grzenda vowed to be a member of the former faction.
Part of a group of six women - the other five were Debbie Miller, Katie Becker, Joni Lawrence, Barb Malone and Teri Oberzan - who came to be known as the "Canyon Girls," Grzenda's group trained for the rim to rim.
Together and separately, they took long hikes around Lawrence and conditioned themselves as best they could for the searing Arizona heat that awaited them at the canyon floor.
On Sept. 14, 2003, the Canyon Girls completed the rim to rim, from south to north, in around 15 hours.
"It was hard," said Grzenda, a former competitive swimmer and longtime high school swimming coach. "I was 50 years old when I did it, so that's a different experience than somebody doing it when they're 25, but for me that was part of the challenge, part of what made it fun. I felt very proud of myself and proud of the group. All I'd ever done before at the Grand Canyon was stand on the south rim and ooh and ahh.
"But this took preparation. It really was a lot harder than I thought it would be. I had nothing left at the end. I'm not trying to scare anybody off, but it was a challenge."
Grzenda paused when asked to compare it to any of her other athletic endeavors.
"I've never done a marathon, so you'd have to ask a marathoner how they compare, but the distance is about the same," Grzenda said. "The speed is different, but a marathon usually doesn't have the elevation change. I was a competitive swimmer, and you train some long hours, but this was a one-shot deal.
"You know, I've done a couple of short-distance triathlons. When I did one in the summer of 2004, the summer after I did the Grand Canyon, I remember standing there, putting my goggles on and saying to myself, 'You crossed the Grand Canyon. How hard could this be?'"
The upside-down mountain
Make no mistake: The rim to rim is no Sunday-afternoon stroll.
Yeston, the ranger, refers to the Grand Canyon as an upside-down mountain, and the metaphor is apt.
Trail head at the north rim is about 8,200 feet, while the south-rim trail heads are around 6,800 or 7,200 feet, depending on the trail.
The inner desert sits around 2,200 feet.
"People pull up to Mount Rainier or Teton and say, 'Hey, let's go climb this thing,'" Yeston said. "They get about halfway up and say, 'This isn't such a good idea,' and turn around. But it's all downhill. Here, you're on one rim and look down. It's nice and cool. You head down. It's easy going. But it gets hotter and drier as you go down. You get to the bottom, and it's 108 degrees, and you still have to go back up. You've got your work cut out for you."
Sometimes it's more work than hikers can manage.
Yeston said there were between 250 and 400 trail evacuations and one or two trail deaths a year. All told, there are 12 to 20 Canyon fatalities yearly, including drownings, homicides and suicides.
Naturally, the rangers would like to cut down on all those numbers.
After a spate of heat-related fatalities in the 1990s, the parks service started a preventative search-and-rescue program, where individuals head down the trails early each day to interact with hikers they encounter.
"We try to turn people around, or adjust people's plans about how prepared they are," Yeston said. "If you're heading to the bottom with a Diet Pepsi can in each pocket, we might try to turn you around. 'This is how much water you need. Those two cans aren't going to cut it.'"
Yeston frequently is asked how best to prepare for a hike like the rim to rim.
"People ask, 'How many hours a week should I do on the StairMaster?'" he said. "For a lot of people, hiking the Grand Canyon is like being on a StairMaster for 12 to 15 hours. Most people don't want to be on a StairMaster 12, 15 hours.
"I tell people, 'You can't just lose the 10 or 20 pounds you're hoping to lose and spend an hour a week on the StairMaster and come here and expect to do a rim-to-rim hike reasonably comfortably. There could be a fit 22-year-old with an ill-thought-out plan to go to the bottom. Are they likely to die? It has happened. It will happen again. One thing I can say with certainty is, you can jam a pencil in your eye socket, but why would you want to?"
Nuts and bolts
Logistics makes up another difficulty in doing the rim to rim.
Snowfall closes the North Rim usually from mid-November to mid-May.
The ideal hiking window shrinks even more when factoring in the peak of the summer heat, thus most rim-to-rimmers aim for early or late-season attempts.
And then there are the travel difficulties once the hike is over.
There is a shuttle service to ferry hikers from one rim back to their cars on the other side, but some eschew the shuttle service in favor of the more arduous rim-to-rim-to-rim hike.
"Those animals who do the rim-to-rim-to-rim : that's just amazing to me," Grzenda said.
In retrospect, Grzenda said, "just" going from one rim to the other was amazing enough.
But, she said, the accomplishment was just part of the payoff.
"The best part of the whole thing, to me, was the way the group pulled together," Grzenda said. "Two people had the idea. One brought in one person, the other brought in two more, they knew somebody who wanted to do it. We didn't know each other real well before we started preparing for it. We trained together and spent many Saturdays doing four-, five-hour hikes around Lawrence and became good friends. It was just a bonding experience with a great group of women, and we've remained good friends."