Tourists are flocking back to the nation's engineering marvels -- the dams, bridges and other structures that had seen increased security and lightened visitor traffic since September 2001 -- even though they are still potential terrorist targets.

Case in point: More than 363,000 people toured the Grand Coulee Dam's visitor center last year, and officials expect at least as many in 2004. Visits to the dam dropped 20 percent after Sept. 11 but have slowly climbed back to pre-attack levels, spokesman Craig Sprankle said.

Authorities at other dams and bridges also have cited a rebound in tourism since it dropped off after the attacks.

Tourists are returning to Hoover Dam on the Colorado River between Arizona and Nevada. Paid visits dropped from 1.2 million to about 850,000 after the 2001 terrorist attacks, spokesman Bob Walsh said. This year, more than 960,000 visitors are expected.

"It's coming back," Walsh said. "As the economy has picked up and tourists return to Las Vegas, ours has gone up accordingly."

The San Francisco Convention and Visitors Bureau estimates that three-fourths of visitors to San Francisco go to the Golden Gate bridge.

Bridge spokeswoman Mary Currie said it is difficult to determine how many visit the Golden Gate because no admission is charged, but tourism appears to be gradually coming back after Sept. 11 and the area's dot-com demise.

Although tourism is recovering, increased security has changed what visitors can do and see.

Traffic across the tops of larger dams, such as Grand Coulee and Hoover, has been restricted or banned. Boats patrol waters nearby, and public areas have been reduced.

At Grand Coulee, guided tours of the giant Third Powerhouse are still offered, although tourists can no longer wander through other areas of the dam. Backpacks and other packages are no longer allowed into the dam's visitor center, Sprankle said.

"Our goal is to make the facility safe for the workers and for the visitors," Sprankle said. "We worked to be able to accept visitors."

Despite the restrictions, people still flock to the structure that was dubbed "the eighth wonder of the world" when it was completed during World War II.

Standing 550 feet tall and nearly a mile wide, the dam has the largest power-producing capacity in the United States. It has been a tourist attraction in north-central Washington state since the late 1930s, when construction was well underway.

Gary Heit, owner of the Coulee House Motel in Grand Coulee, said bookings fell off after the attacks but have been building steadily since. Few guests ask about potential terrorism, but some have questions about parts of the dam that have been off-limits since the attacks.

"People realize what's happening," he said. "They get to go down to the powerhouse and see the dam, and that's what they hoped to do."

Visits to the Grand Coulee Dam in Washington dropped 20 percent after the Sept. 11, 2001, attacks but are slowly returning to pre-attack levels.