The Tucson Convention Center is holding a stair climbing challenge to honor those first responders who served and died on September 11, 2001.

Over 1,000 people signed up to participate in the 9/11 “Never Forgotten Memorial Tower Challenge.”

Formal opening ceremonies began at 7 a.m. Monday.

The challenge is to climb 2,071 steps; it represents the 110 stories of the World Trade Center Towers. Many first responders who participate climb in full gear.

The event is organized by the non-profit 9/11 Tower Challenge Foundation. All proceeds will go towards first responder and military charities in Southern Arizona.