The noise at ground zero is a steady roar. Engines hum. Cement mixers churn. Air horns blast. Cranes crawl over every corner of the 16-acre site.
For years, the future has been slow to appear at the site of the Sept. 11, 2001, attacks. But with six months remaining until the national 9/1 1 memorial opens, the work to turn a mountain of rubble into the inspiring site envisioned nearly a decade ago is thundering forward.
One World Trade Center, otherwise known as the Freedom Tower, has joined the Manhattan skyline. Its steel frame, already clad in glass on lower floors, now stands 58 stories high and is starting to inch above many of the skyscrapers that ring the site. A new floor is being added every week.
The mammoth black-granite fountains and reflecting pools that mark the footprints of the fallen twin towers are largely finished. Workers have already begun testing the waterfalls that will ultimately cascade into a void in the center of each square pit.
About 150 trees have been planted in the plaza that surrounds the fountains and pools.
The plaza won't be complete when the site opens on Sept. 11, 2011, and a tour of the site last week makes clear that work around it will continue for years. Mud is still plentiful at ground level, and for now the site is dominated by the same concrete-gray shades that blanketed lower Manhattan after the 9/1 1 attacks.
But the agency that owned the trade center and has spent nearly a decade rebuilding it is aiming to deliver a memorial experience on 9/1 1/1 1 that closes one chapter -- marked by mourning -- and ushers in a new experience, where ground zero again becomes part of the city's everyday fabric.
"We want people to be able to see that downtown does have this incredible future to it," said Chris Ward, executive director of the Port Authority of New York and New Jersey. "The work will not be done on that day. What we hope will be done is the sense of frustration."
Workers labor around the clock. During the busiest shifts, about 2,800 people labor amid tangles and ravines of steel. In one steel cavern that will become a transit hub concourse, showers of orange sparks fly as welders install trusses weighing up to 50 tons.
From the top of One World Trade, the view is spectacular, as it was from the twin towers, even though the building stands at 680 feet, less than halfway to its planned 1,776-foot height.
By Sept. 11, the building is expected to be 80 stories high, the tallest tower downtown.
A huge portion of the reconstruction of the trade center is taking place below ground. The underground halls that house the memorial are cavernous.
The 60-foot-high slurry wall of reinforced concrete on the western edge of the site, meant to hold back the Hudson River, bears similarities in size and appearance to the Western Wall in Jerusalem.
The huge boxes that hold the waterfall pits visible from the surface are somehow suspended from the ceiling, held up by pillars that don't seem big enough to support the blocks' massive weight.
A maze of tunnels, catwalks and narrow, temporary staircases connect the various underground levels.
The tunnel holding Manhattan's No. 1 subway tracks was buried beneath a mountain of rubble after the attacks. The tube now runs right through the middle of the site, hurtling thousands of passengers through ground zero every day.