Transcript for Nik Wallenda and sister Lijana to perform stunt 25 stories above Times Square
The countdown is on for what could be the stunt of the century. 25 stories above New York City's times square, NIK Wallenda and his sister lijana attempting a fantastic feat and rob is in times square with more on that. That wire must look way up there from where you're standing. It does look that way and I imagine it looks even higher when you're standing on top. It's going to start at 1 times square basically just below where the ball drops on new year's eve. That is where lijana is going to start and she's slowly going to make her way uphill basically. Take a look at our second camera, you'll see the center of this high wire. It stretches 1300 feet, has a steady incline. NIK will then cross and climb over her during the middle of the stunt which will take 35 minutes basically while hundreds of thousands of people on the ground and millions across the globe watch live on television. NIK Wallenda seen here taking a few practice steps on the high wire Saturday, preparing for his death-defying stunt in times square, now just hours away. Tonight, the brother/sister daredevil duo, Nick and lijana, make history on this high wire, 25 stories up, 35 feet long. Trading places in the middle. If that's not daunting enough -- One of the challenges we have is we're at 17 stories here but 25 stories there. Reporter: An 8-story incline, adding another heart-pounding obstacle. This will be their first live performance together since lijana was injured in this devastating high wire accident back in 2017. She and four others falling from a wire while rehearsing to set a world record. Lijana seen here in the pink shirt shattered every bone in her face. The memory of the accident leaving her shaken. When she gets up there, I don't know that she'll take that step. The last time I was up that high, my worst nightmare came through. Reporter: That didn't stop her from taking that step on the wire. She wanted the close the circle that was left open from that accident. Reporter: Even upping the ante. Taking the wire two times higher and four times longer than anything lijana has done before. I am nervous, I'll tell you the truth. Reporter: Though brother NIK has wowed us before with wild high wire stunts from the grand canyon to niagara falls, he says times square is a whole other animal. I've done some big events in short periods of time but nothing compares to this. Trying to get a feel for what lijana might be going through later on tonight. My heart goes out to her after that terrifying fall, what she's going to feel like. Al, don't -- don't pan out, Al. I don't want to give away the secrets here, guys. This is going to be -- I mean, I can't imagine. What an amazing spirit and wiring these guys have to be able to do this tonight. It's going to be something to watch as they do it live on television. Guys, back inside to you. We're all going to be holding our breath. I had confidence in them until I saw your wobbly maneuver up there and that made me even more nervous for what they're about to pull off. That was dad humor at its best. And we loved every second of it. Thank you, rob. Appreciate it. Of course, tune in tonight starting at 8:00 P.M. Eastern for this can't-miss event. "Highwire live in times square with NIK Wallenda" right here on ABC.
This transcript has been automatically generated and may not be 100% accurate.