Urban photographer Roman Robroek spent five years scouring the continent for the grandest examples of forgotten architectural beauty. Here: Watch your step on this Polish spiral staircase. (Photo by Roman Robroek/South West News Service)

People gather on a hill near the Chopin Airport to watch aeroplanes taking off, in Warsaw, Poland, Sunday, September 9, 2018. (Photo by Alik Keplicz/AP Photo)

Girls watch a procession during the “Fiesta de las Palancas” celebration to ask for blessings and abundance during the new year in Panchimalco, El Salvador, January 5, 2017. (Photo by Jose Cabezas/Reuters)

A boy watches fireworks from a military range weapon, marking the Defender of the Fatherland Day celebrations, at the Artillery Museum in St. Petersburg, Russia, Thursday, February 23, 2023. (Photo by Dmitri Lovetsky/AP Photo)

A fan watches the pre-game before an NFL football game between the Indianapolis Colts and the Tampa Bay Buccaneers Sunday, November 26, 2023, in Indianapolis. (Photo by Darron Cummings/AP Photo)

Tourists watch roaring torrent carrying a large amount of yellow sediment at the Hukou Waterfall on the Yellow River on August 15, 2024 in Yan'an, Shaanxi Province of China. (Photo by VCG/VCG via Getty Images)

Revelers celebrate New Years Eve in socially distanced pods at Times Square on December 31, 2020, in New York City. On average, about one million revelers are drawn to the Crossroads of the World to watch performances and celebrate the New Year. This year a limited live audience of about 40 first responders and essential workers will be allowed to watch the New Years' ball drop from a secure area in Times Square. (Photo by David Dee Delgado/Getty Images)

An Armatix employee holds a “smart gun” by the company at the Armatix headquarters in Munich May 14, 2014. The gun is implanted with an electronic chip that allows it to be fired only if the shooter is wearing a watch that communicates with it through a radio signal. If the gun is moved more than 10 inches (25 cm) from the watch, it will not fire. A Maryland gun shop owner has dropped his plan to be the first in the United States to sell the so-called “smart gun” after a backlash that included death threats. (Photo by Michael Dalder/Reuters)