(NEW YORK) -- Acrobat siblings Nik and Lijana Wallenda, along with a crew of workers, are making final preparations for an epic high-wire stunt in the middle of Times Square.
On June 23, the daring duo will walk one of their most challenging routines to date between two New York City high rise buildings 25 stories -- more than 1,000 feet -- in the air.
ABC News has learned that the rigging process came with difficulties for the production crew.
"It's always changing -- it makes it a nightmare -- so you never know what's going to happen," Nik Wallenda told ABC News.
The executive producer of Sunday night's show told ABC News the race to install the wire rig "proved more challenging than Nik ever imagined" and that his "team will be making adjustments to it all week because there is zero room for error."
The two-hour televised event marks Lijana Wallenda's first high-wire walk since an accident in 2017 when she, along with four other acrobats, fell off a tightrope during a rehearsal.
"I broke a rib, punctured my right ear canal, broke clear through my left humerus, I broke my left calcaneus," she said. "But the big one was every bone in my face."
The siblings, seventh-generation members of the Wallenda family circus troupe, have trained for the worst possible conditions. They've used wind machines with 90 mph winds and hoses blasting water to simulate torrential rain.
"I've done some big events in short periods of time, but nothing compares to this," Nik Wallenda said.
Two years since the tragic accident, Lijana Wallenda will have to confront her nerves before the physical and psychological challenge.
"I'm just a little nervous because the wire moves more than anything I've ever been on," she explained.
The siblings will start on opposite ends between the famed between the famed 1 Times Square and 2 Times Square, and the most harrowing moment will be when they cross each other in the middle of the wire with live crowds watching from below.
Highwire Live in Times Square with Nik Wallenda will air live on Sunday, June 23 8:00 to 10:00 p.m. ET on ABC.
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