One by one, they slung themselves over the side of a 21-story Center City building and rappelled down its sleek surface.

On Friday, about 70 daring Philadelphians, including Mayor Michael Nutter, were handed a helmet and strapped into a harness at the top of 1515 Market St. as part of a fundraiser to support Outward Bound Philadelphia.

The world's oldest and largest adventure-based educational program teaches character building and leadership to underserved students attending local public and charter schools.

Katie Newsom Pastuszek, executive director, said "Building Adventurer 2012" was dreamed up to give the organization some exposure and to show each participant the power within them.

"What we are hoping they realize is that if they are properly coached and instructed, that they can do something that they always thought was impossible and they can overcome challenge and recognize that inside of them there is something more than they had seen before," said Newsom Pastuszek.

Mayor Nutter, who helped found Outward Bound Philadelphia, climbed to new heights on the campus of Temple University Center City just after 2:30 p.m. on Friday.

With arms outstretched and City Hall at his back, he posed for occasional pictures and waved to employees safely working on the other side of the glass.

Though he admitted to thinking, " ' Wow, I just stepped off the ledge of a 21-story building,' " before he began his long trek down the face of the towering building, Nutter said the benefit of the event outweighed any fear.

Chestnut Hill resident Nancy Goldenberg followed Nutter. She was provided with words of encouragement - "way to go Nancy and " you can do it" - almost immediately.

In a crowd of more than 100 onlookers, a small cheering squad watched her journey on a television screen.

Goldenberg, one of the founders of Outward Bound Philadelphia, said the fundraiser directly correlates with the experience-based learning that the organization hopes encourages and helps participants in all aspects of their lives.

" The wilderness experiences are really metaphors for life experiences," said Goldenberg. "It is through nature - paddling, mountain climbing - that you learn to become a leader and how to navigate in tough situations and you are going to face those tough situations when you are in a classroom, in an office and all through the rest of your life."

The event was not Goldenberg's her experience with rappelling, but it was first time she tackled anything so tall. She's already looking forward to next year's event.

"Maybe we should jump off the Comcast tower,” joked Goldenberg,

The monetary goal of the day was to raise $160,000, which required each thrill-seeker to raise $2,000 or more to rappel.

As of Friday evening, the first-time event has pulled in $157,000.