It's a scramble to the top.

But about 700 people will try, taking the long way up to the 72nd floor at 4 World Trade Center on Thursday — climbing the stairs.

It's called the "Runyon Up," and it's a fundraiser for the Damon Runyon Cancer Research Foundation.

The event will start with elite climbers, who will head off first. The general field will go up after that, with climbers heading off one at a time every few seconds.

Participants can either do a full climb, all 72 floors, or a partial climb to the 54th floor. There's also a virtual climb, for those who want to take the elevator to the 54th floor.

The event is sanctioned, unlike a recent spate of thrill-seekers making unauthorized visits to the site.