Running across the country certainly isn't an easy feat.
But imagine doing it without shoes!
That's what one 18-year-old Indiana woman is doing right now.
David McCoy explains why she's doing it.
With nothing but the backpack on her back, Rae Heim has already run nearly a thousand miles through 11 states.
And she's almost halfway to her destination.
"The first day I did 44 miles. It was about the fourth day when I wanted to completely stop. But, when things start getting difficult I just think about why I'm doing it. And it makes it worth it."
Rae is running across America.
She went all the way from Warsaw to bourbon on the day we caught up with her, which is impressive not only because that's 17 miles, but because she's hard to catch up with.
(Reporter): "How do people look at you when you tell them what you're doing?"
"Once it sinks in, they kind of give me strange looks and are like, 'Dude, you're crazy.'"
Not only is Rae running across the entire country, she's doing it barefoot-- for a charity called soles4souls.
"I was running barefoot so others don't have to. Every dollar that gets donated to the charity, someone will get a pair of shoes."
"It's actually way more comfortable for me to run barefoot than with shoes on. So, that part's not actually that difficult for me. But I guess the most difficult part is just waking up and going to sleep every night knowing that I have to get up and run 20 to 22 miles each day."
When she gets tired, she walks.
And when it's necessary, she puts on shoes.
"The cement was starting to get so hot that it was kind of melting onto my feet."
And still, she runs on.
"I ran through the Bronx in New York City and nothing since then has fazed me much."
But when she needs encouragement...
It's always just a few steps ahead.
"I kind of enjoy looking at the map, and just seeing that I've come a decently far way. Now, I'm like, I can't give up, even if I wanted to. Just 'cause I've gotten this far."
Heim started her journey in Boston back in April.
She's expecting it to end in Southern California in November.