New York City Mayor Michael Bloomberg gets on a custom made World Trade Center inspired motorcycle in front of the 9/11 Memorial Preview Site on October 5, 2011 in New York City. The motorcycle was designed by Paul Teutul Jr. of the television show “American Chopper” and was built to commemorate the rebuilding of the World Trade Center Site. Another motorcycle, nearly identical to the one unveiled, will also be built by Paul Jr. and raffled to raise money for the 9/11 Memorial. (Photo by Spencer Platt/Getty Images)

Men wearing costume of traditional firefighters perform acrobatic stunts atop a bamboo ladder following a memorial service for firefighters at Sensoji temple in Tokyo's downtown of Asakusa May 25, 2015. Hundreds of firefighters in traditional costume gathered on Monday for the memorial service for firefighters who were killed performing their duties during the past 300 years. (Photo by Issei Kato/Reuters)

Final match Soccer Humanoid Kid Size between DARwIn vs. AUTMan at the World Championship finals of RoboCup 2013 in Eindhoven (NL). (Photo by Bart van Overbeeke)

Runners gather at the start line for the annual “Santa Speedo Run”, a charity race through the streets of the Back Bay neighborhood of Boston. (Photo by Gretchen Ertl/Reuters)

Members of the 3rd U.S. Infantry Regiment place American flags at the graves of U.S. soldiers buried at Arlington National Cemetery in preparation for Memorial Day May 26, 2011 in Arlington, Virginia. “Flags-In” has become an annual event since the 3rd U.S. Infantry Regiment (The Old Guard) was appointed an Army official ceremonial unit in 1948. Every available soldier in the 3rd U.S. Infantry Regiment participates in these annual ceremonies. (Photo by Win McNamee/Getty Images)

The Mike O'Callaghan–Pat Tillman Memorial Bridge is an arch bridge in the United States that spans the Colorado River between the states of Arizona and Nevada. The bridge is located within the Lake Mead National Recreation Area approximately 30 miles (48 km) southeast of Las Vegas, Nevada, and carries U.S. Route 93 over the Colorado River.

A woman participates in the “Carnaval na Central” block party in Rio. (Photo by Felipe Dana/Associated Press)

Burning Man 2013. The federal government issued a permit for 68,000 people from all over the world to gather at the sold out festival, which is celebrating its 27th year, to spend a week in the remote desert cut off from much of the outside world to experience art, music and the unique community that develops. (Photo by Neil Girling)