High-wire artist Nik Wallenda has just completed a daring double-challenge by walking up a steeply-inclined tightrope some 190 metres across the Chicago river, suspended 150 metres above the ground.
The footage, aired on the Discovery Channel, ran on a 10-second delay so producers could cut away if he fell to his death. He had neither a net nor a harness while he completed the feat - his only back-up plan if things went wrong was to attempt to kneel and cling to the wire with his feet.
He finished the first portion of the stunt in six minutes, 52 seconds. The second part of the challenge was a blindfolded high-wire walk between the west and east Marina City Towers to come. He has always said that will be the biggest challenge.
The first wire was suspended above the Chicago River at a 19-degree incline. The wire was supposed to be suspended at 15 degrees, but a last minute change made for an even steeper challenge. On the blindfolded portion, Wallenda will shuffle his feet rather than lifting them. A pinging sound at his destination will help guide him.
The Windy City is earning its name this evening, with speeds capable of exceeding 30mph during the attempt, and temperatures could dip as lower than 40 degrees. The unpredictable gusts swirling around Chicago's skyscrapers mean gusts could approach from any direction.
Wallenda, a member of the Flying Wallenda tightrope-walking family, has success in his blood - but also failure. His great-grandfather Karl Wallenda fell to his death in a tightrope-walking stunt in Puerto Rico, aged 73. Ahead of the attempt he said: "Just looking at it is extremely intimidating."
The daredevil's challenge started just after sunset, with the skyscrapers up and down the Chicago River lit up and sparkling.
He has now walked uphill at a 19-degree angle from the Marina City west tower to the top of a skyscraper on the other side of the river. Next, he'll walk blindfolded between the two Marina City towers.
If he slips, Nik will attempt to grab the wire as he falls, at which point rescuers will be able to slide down the wire to catch him. He says that he can cling on to the wire for as long as 30 minutes waiting for rescue.
Earlier he had spoken exclusively to MailOnline, revealing how he would be bound for death and failure without the unwavering support of his family.
The Wallenda clan have been tightrope walkers for generations - and witnessed Nik's great-grandfather Karl plummet to his death aged 73 while walking between two buildings in Puerto Rico.
Speaking a week ago from his home in Sarasota, Florida, he said: "It is key to my success to have that support. If I didn't have my mom and dad's support and my wife's support I wouldn't be able to make that walk."