ARLINGTON — Up until three years ago, Sandy Catiis’ biggest climb was up a 20-foot rock wall.

Next month, she will be making her way down the side of a 500-foot skyscraper.

Catiis, an Arlington resident, will join about 100 participants in the Special Olympics Washington’s “Over The Edge” fundraiser at the 40-story Rainier Tower in downtown Seattle on Saturday, Aug. 14.

Organizers are hoping to raise more than $120,000 for about 7,500 Special Olympics athletes in Washington.

The event is fairly simple — participants strap into a full-body harness and a helmet and rappel from the top of the building down to the street.

The hardest part, Catiis said, is that first step across the building’s edge.

“Once you’re at the top, you don’t have anywhere else to go but down,” she said. “Just getting over the edge is the worst.”

Although the event will be a challenge, Catiis has plenty of motivation.

The 49-year-old’s son, 22-year-old Justin, has autism, and the family has been organizing and participating in Special Olympics competitions since 2003.

Catiis has been the head coach for the Arlington Eagles Special Olympics team for the past six years.

“The push behind doing (Over The Edge) is for my team,” she said. “I see such a tremendous difference in them when they’re competing. But I also wanted to do it for my own personal experience.”

Catiis had to raise at least $1,000 — a number she has reached thanks to two donations — in order to rappel down Rainier Tower. She said she’s hoping to reach $5,000 in donations, adding that community members can donate to her cause by visiting her Special Olympics Washington website at www.firstgiving.com/sandycatiis.

Special guests at Over The Edge include John Curley, Seattle resident and former host of KING 5 television program “Evening Magazine,” and Sue Ershler who, with her husband Phil, became the first couple to climb the seven highest summits on each of the seven continents.

Catiis said she’s hoping that members of her team will be able to make the trip down to Seattle and watch her climb down the building.

Her other son, 17-year-old Mike, will also be nearby for support.

“I’m not a very competitive person — for me, it’s all about the fun and the experience,” Sandy Catiis said. “I coach the same way. It’s a different mindset to get athletes to compete against themselves not against each other.

“Having Justin, we can’t do a lot of traveling, and sometimes I can’t be out there making a difference. But Mom can climb down a mountain.”