It is also ranked the fourth best triathlon in the world.
Local triathlete and member of Skegness Triathlon club, Michyla Clark travelled to San Francisco to take on the challenge.
Sunday saw 2,000 athletes start the annual Escape From Alcatraz Triathlon which is now in its 41st year.
It is still the scariest-sounding triathlon, named after the former maximum-security prison.
The infamous race start has competitors leap into the San Francisco Bay from a passenger steam boat parked near Alcatraz Island.
That’s followed by a breathless 1.5-mile swim to the deceivingly distant Marina District shore of San Francisco through dark, choppy 12 degree water with treacherous currents and the odd laughing sea lion.
The open-water swim is like no other in the world, and one of the most difficult in the sport.
It’s like crossing a rapid racing river with millions of gallons of water flowing out under the Golden Gate Bridge.
Michyla had to mentally prepare for the jump from the ferry and the tough swim and she physically prepared through completing mang sea swims off Skegness beach with other tri club members and her dad.
After the leap from the ferry things soon settled down and Michyla got to enjoy the sight of Alcatraz island from a unique perspective.
The remaining two-thirds of the triathlon include touring some of the prettiest corners of San Francisco’s Presidio and Golden Gate National Recreation Area on an 18-mile bike course full of brutal hills and turns, and then running a punishing eight-mile multiterrain course on pavement, grass, dirt, beach and a tough set of cliff stairs called the Sand Ladder.
The sand ladder is a steep set of 200 steps on very wobbly legs, you know it’s going to hurt.
For Michyla, this iconic race was a bucket list challenge, a once in a lifetime opportunity after being allocated an entry in the race draw.
"It’s an incredible triathlon with unpredictable conditions in the most amazing setting," she said.
The challenge was made even harder after Michyla suffered a severe back injury in December 2021 and was completely out of action for three months.
It was the thought of competing in San Francisco that kept her motivated to recover.
Her race time was 4 hrs 22 mins.