CHICAGO — For many tourists, the Chicago skyline is best viewed from Willis Tower's Skydeck Ledge, their feet appearing to float above the city below, but firmly, securely planted on glass.

Bradley Garrett would rather go without the glass.

Garrett is a University of Oxford researcher and self-described "urban explorer" who has made a career out of photographing his adventures in going places you're not supposed to — including dangling his feet off the edge of the 72-story Legacy Tower overlooking Millennium Park.

Chicago is Garrett's favorite American city, and his time spent climbing to the top of several Chicago skyscrapers in 2011 is detailed his new book "Explore Everything: Place-Hacking the City."

Bradley Garrett is a University of Oxford researcher and "urban explorer," who describes climbing to the top of Chicago's skyscrapers in his new book "Explore Everything: Place-Hacking the City." View Full Caption ©Bradley Garrett/eyevine/zReportage.com via ZUMA Press

"Urban explorers, much like computer hackers in virtual space, exploit fractures in the architecture of the city," writes Garrett, who is originally from the Los Angeles area. "It is both a celebration and a protest."

For his tour of Chicago, Garrett had hoped to explore now-unused tunnels beneath the Loop, but found that American nosiness derailed his plans.

"Chicago is busy — and unlike London, where people will ignore you doing something naughty, or Paris, where people will ask to come with you — in Chicago people will actually stop in the street at 2 a.m. and ask you why you are prying open a manhole and who you work for."

So he settled for the skies.

With a fellow explorer, Garrett started at the 30-story Hilton Chicago, 720 S. Michigan Ave., where he popped open the doors from the elevator control rooms with a credit card and climbed the fire escape to the roof.

"But the Hilton's rooftop, sexy as it was, left us unsatiated, since it put us eye-level with the torsos of taller buildings," he wrote in "Explore Everything."

So Garrett climbed higher, to the 40th story of the then-unfinished Ritz-Carlton Residences, 625 N. Michigan Ave., and the roof of the 72-story Legacy Tower, 60 E. Monroe St.

During the Ritz-Carlton climb, Garrett was trapped in a nightmarish storm, but his fear was overshadowed by the "stunning" view of lightning piercing the skyline.

"The photos we took that night, of my favourite American city bathed in black cloud and blue light, standing on ledges with lightning strikes crawling down from the clouds into Lake Michigan, the storm slowly creeping away, captured the most beautiful moments I had seen yet in North America," he wrote.

Though Garrett sneaked past security guards and jimmied doors with credit cards to get his photos, he said the Legacy Tower public relations department didn't find the publicity all bad. A representative asked if he could put a link to its website on his blog, where he wrote about his "place-hacking" of Chicago, Garrett said.

The Legacy Tower declined to comment for this story.

Garrett also has opened a hatch to hang out beneath a Chicago River bridge, and explored the building that used to house Brach's Candy Factory at 401 N. Cicero Ave. in Austin.

Though vacant since 2003, "[T]he whole factory reeked of marshmallows, nuts and chocolate," he wrote on his blog.

"If Place Hacking was scratch and sniff, I could have bottled and relayed the smell of derelict chocolate," he said. "Since we haven’t uncovered that particular technological wonder just yet, you will have to ... climb over that fence yourself."