NEW YORK - Exactly 10 years ago, ground zero was a smoking, fire-spitting tomb, a ghastly pile of rubble and human remains. On Monday it was a place of serenity - an expanse of trees and water in the middle of a bustling city - as the 9/11 memorial opened to the public.

As they walked through a grove of oaks and traced their fingers over the names of the nearly 3,000 dead, visitors were deeply moved by the monument, whose centerpiece is two sunken pools ringed by bronze plaques.

"When we walked in, those images were popping in my head from 10 years ago," said Laura Pajar of Las Vegas. "But when I saw the memorial, all of that went away. This is so peaceful, and you kind of forget about what happened and you look toward the future."

About 7,000 people registered online for free tickets to visit on opening day, and 400,000 are signed up for the coming months, according to the nonprofit organization that oversees the memorial.

Many visitors made pencil-and-paper rubbings of the names to take back home. Others sat on benches or clustered for photos. Some people cried; others embraced. Some left flowers or stuffed messages into the letters.

"There were no words," Eileen Cristina of Lititz, Pa., said as she wiped away tears. "The enormity of the loss, the enormity of human kindness, the enormity of the suffering."

The site was opened on Sunday - the 10th anniversary of the Sept. 11 attacks - to the 9/11 families. Monday marked the first day since the tragedy that ground zero was opened to the public.

Security was airport-tight, with visitors forced to empty their pockets, go through a metal detector and send their bags through an X-ray machine.

The memorial takes visitors on a kind of journey. First they walk through a promenade of more than 200 white oak trees. Then, like hikers coming upon a canyon, they arrive at two 30-foot-deep pits on the exact spots where the World Trade Center's twin towers stood. Water cascades into the two voids, evoking the dust cloud that accompanied the towers' fall.

The falling water creates a constant whooshing, muffling the noise of the city and nearby construction.

"It's like an entrance to eternity," said Wojtek Ballzun, a rail worker from Warsaw, Poland.

Jim Drzewiecki, a retired volunteer firefighter accompanying a current team of them from Lancaster, N.Y., said he was trembling as he stood next to the pools.

"I'm actually still shaking," he said. "It could have been me on that flight. On any one of the flights. ... There's not much that separates us."

The bronze plates carry the names of the 2,977 people killed in the terrorist attacks in New York, at the Pentagon and in Pennsylvania, plus the names of the six who died in the bombing of the trade center in 1993. The letters have been cut all the way through the metal, with empty space beneath them.

Nearby are a half-dozen electronic directories to help visitors find names, which are grouped not alphabetically but in ways that show the connections between co-workers, firefighters, airplane flight crews and other victims.

The memorial's architect, Michael Arad, said the plaza next to the pools was inspired by gatherings of mourners that he saw in New York's Washington Square and Union Square after the attacks.

"These places don't just bring us together physically in one spot, they brought us together emotionally," Arad said. "We've recreated that opportunity for that to happen here."

There is a separate entrance for 9/11 family members and comrades of the fallen firefighters and police officers. Certain days or hours will be set aside for them to visit privately.

Workers are still building the 9/11 museum underneath the memorial. It is scheduled to open in 2012 and will include two of the forklike supports that were left standing when the World Trade Center fell, as well as a stairway that enabled hundreds to escape.

Construction also continues next door on 1 World Trade Center, still called by many the Freedom Tower, which is more than 80 stories high so far and will be the nation's tallest building at 1,776 feet.

It is one of several new buildings that will eventually surround the memorial. Two World Trade Center will be 1,349 feet high with a diamond-shaped tip and an 80-foot antenna. The 53 stories of 3 World Trade Center will feature crisscross external braces.

Admission to the memorial is free, but visitors must obtain passes in advance that allow them to enter at a specified time.

The cost of the memorial and museum has been put at about $700 million. The nonprofit organization that runs the project has raised about $400 million in private donations and is seeking federal funds.

Jim Brown lost his brother-in-law, Kevin Bracken, and two other relatives on 9/11. He said he felt cheered after seeing Bracken's name permanently on the memorial.

"They never found Kevin," Brown said. "To me his spirit is all over here. ... His spirit will always be here in this part of Manhattan."

Associated Press writer Chris Hawley in New York contributed to this report.