Most people, you would imagine, would celebrate their 63rd birthday by relaxing with friends and family - perhaps even with a party.
You don't imagine they'd be swimming into the Florida Keys, having set off from Havana a couple of days beforehand. But that's exactly what Diana Nyad is trying to do - and aiming to set a record in the process.
The writer and noted distance swimmer set off at the weekend for her third attempt in a year to swim from Cuba to Flordia without the aid of a shark cage. The last two attempts last summer failed, notably due to jellyfish stings which affected her ability to breathe.
By the early hours of Tuesday morning, she had covered around 60 of the 103 miles separating Havana from the Keys. Behind schedule, a storm had blown her off course on Sunday night, but gulf stream currents on Monday had helped make up some of the lost time.
And the jellyfish have been back. Most folk, by this point, would surely have jacked the whole venture in and gone back home to enjoy some birthday cake.
The challenge is keeping her body in a state where it can handle the swim. Although she takes short breaks to rest and hydrate, the water is about 85 degrees - lower than that of her core temperature - and her support team have been improvising ways to prevent her contracting hypothermia.
"Diana has historically been known as much for her mind as for her athleticism," team member Candace Hogan wrote on the swim's blog yesterday.
"We all know her mind can handle it. But there will always be a point where a human body can’t go any farther. What no one knows is where that line is drawn in Diana Nyad."
Nyad has completed a similar swim before - more than 30 years ago, on her 30th birthday, when she set a world record by swimming between North Bimini Island in the Bahamas and Juno Beach in Florida. Then, as now, she did not use a shark cage.
The route she's taking has been swum before, but only with the use of a cage, while other attempts have fallen short - stymied by the currents between the two coasts.
The swim is being carried out to raise awareness of the Natural Resources Defense Council, an environmental body which is campaigning to protect dolphins and other sea creatures. And as if to indicate the creatures whose plight she aims to highlight were backing her efforts, the team posted a remarkable video shot last night of dolphins joining Nyad on her swim.
Fingers crossed she completes the remarkable swim. Swimming non stop for 100-plus miles is an achievement at any age, let alone on the eve of your 63rd birthday - and proves there are truly few things the human spirit cannot conquer.
UPDATE: Sadly, Diana Nyad didn't complete the swim - a heavy storm forced her to abandon the swim for safety reasons.