"It's kind of freaky. I'm terrified of heights. I'll bet everything looks all swirly up there," said Brandon Guy, 14, of Windsor, Calif.
Engineers said that the 1884 landmark is structurally sound but that they need to catalog every defect so they can determine how long it will take to repair it and reopen it to the public.
To carry that out, they called in a "difficult access team" of specialists certified in both architectural engineering and climbing. The team was supervised by a park ranger with extensive mountaineering experience in the Denali National Park in Alaska, home to North America's highest peak.
During the daredevil inspection, which is expected to last several days, the intrepid climbers will work their way up and down the sides of the entire monument, snap photos with a digital camera and tap the stones with a soft mallet, listening for indications of damage.
They have masonry tools to remove loose stone or mortar. Each is also carrying a two-way radio and an iPad loaded with data from the 1999 restoration of the monument.
Deb Blanchard drove to Washington from her home in Palmyra, Pa., to watch her brother, Erik Sohn, rappel down the face of the tallest structure in Washington and one of the most recognizable landmarks in the world.
"This doesn't make me feel very good right now. I've got to be honest about that. Wow!" she said. But she said her brother wasn't nervous: "He's a very responsible, meticulous, careful kind of person. This fits his personality. It's such a fantastic opportunity for him."
Sohn's wife, Schalyn, came from the couple's home in Chantilly, Va., bringing their infant daughter and 3-year-old son, Schaffer, who dressed for the occasion.
"I explained that Daddy is being like Spiderman, climbing on the building today. So he is wearing his superhero Spiderman shirt," she said.
Sohn and the other team members are part of a relatively small group that can do such precise work at dizzying heights. Still, more than one described it as a once-in-a-lifetime experience.
The team also includes 32-year-old Emma Cardini of Melrose, Mass., who has rappelled down columns on Panama's Bridge of the Americas, dangled from rope inside the Old South Church in Boston and inspected the Gothic spires at the top of Chicago's Tribune Tower.
An engineer with degrees from Tufts University, she keeps a hard hat in the back of her car and has "zero fear of heights," said her husband, A.J. Cardini, himself an engineer.
The assignment came at a tricky time for the couple, who just moved into a new home and are trying to sell their condo. Their real estate agent texted her yesterday: "hi! You have an offer. Can u talk?"
Her response: "not really... I'm on the top of the Washington Monument getting ready to rappel, and service is not great."
National Park Service officials hope to announce a timetable by mid-October for repairing and reopening the monument. The inspection is being done by the engineering firm Wiss, Janey, Elstner Associates Inc. of Northbrook, Ill.
The monument sustained numerous cracks during the 5.8-magnitude quake that rocked the nation's capital last month, and it has been closed to visitors ever since.
Daylight can be seen through some of the cracks, the largest of which is 4 feet long and an inch wide. Inside the obelisk, pieces of stone and other debris rained down during the quake.
Around the National Mall, bystanders watched the climbing engineers intently.
Kristen Dudacek, of St. Paul, Minn., said she came to watch two days in a row, jokingly describing herself as a "rappel groupie." But she added: "It's not something I would ever do."
"I'm impressed with their courage, agility, nerves," said Randy Walker, of Lenoir, N.C. "I bet they get paid very well. I wouldn't find fault with that government check."