A marathon is considered one of the most enduring challenges a runner - or anyone - can take on, with anyone who has ran the gruelling 26.2 miles (42km) able to tell you that it's not just physically tough, but it also takes its toll mentally.
However, one man has decided to run not just one marathon, but a whopping 196 - one in each country in the world - to raise funds for charity.
Nick Butters, who has been a professional runner for around five years, was taking part in an ultra-marathon in the Sahara Desert in 2016 when he met a man called Kevin Webber, who would inspire him to take on the Herculean task.
Speaking to LADbible, Nick says: "[Kevin] and I just really got on, he was one of those incredibly inspirational people without really having to say much. He dropped this bombshell on me that he had terminal prostate cancer.
"It was such a shock because he was such a happy, overly-enthusiastic guy. We had these amazing conversations in the desert - it was an incredible week. I came away thinking, 'You know what? Life is short.'
"I was already following my dreams and doing something I loved by running. So I thought, 'Let's try and do something that will raise money for prostate cancer and for Kev.'
"It quickly spiralled into wanting to set a world record - to do something that was big enough to capture people's attention and raise a lot of money."
So that's what he did. Nick decided to plan a worldwide trip where he would take on a marathon in all 196 countries, while setting himself a challenging £250,000 target for Prostate Cancer UK.
After spending months planning, Nick set off almost two years ago, heading to Canada for his first marathon.
Fast forward 675 days, Nick says he's worked his way through 10 passports, smashed eight world records, taken over 200 flights and tread more than 10 million steps. I feel tired just thinking about that, mate.
Along the way he's met thousands of people, as he explains: "The amount of amazing people I have met through this trip... I can't even begin. I ran with a thousand people in El Salvador and they were all just people who came out, it wasn't a special race.
"I've had hand-carved medals made with my face on. I have ran past and around an erupting volcano in Guatemala... there's so many brilliant memories."
And the challenges? Well, where do you want to start? Nick's battled with extreme temperatures at both ends of the spectrum - highs of 60C in Kuwait and lows of -25C in Canada - he's also been attacked by dogs and, perhaps most scarily of all, robbed at gunpoint while in Nigeria.
And if that's not bad enough, he adds: "I've had food poisoning eight times. Still having to run while dealing with that is rough. I threw up about 12 times while running in Bangladesh. I've also had a really painful tooth infection and a kidney infection - you name it, I've been through it!"
Alongside this he was also dealing with extreme exhaustion, getting by on as little as three hours' sleep a night and having 'no idea what time it is, what day it is or even what country I'm in'.
Despite all that, it never occurred to Nick to give up. Now, not only is he the first person to ever run a marathon in every single county in the world, but he's also raised a bunch of cash for a really good cause. However, he's still got a little bit to go to reach his target, so why not help him out by clicking here?
As for his future plans, Nick says firstly he's going to get some kip - fair enough - and he's also put on a big celebration in Athens, where he ran his final marathon, for friends and family.