Photo taken on Jan. 4, 2019 shows the downtown Cologne, Germany, with the Cologne Cathedral in sight. Construction of Cologne Cathedral began in 1248 and was eventually completed in 1880. The total area of the Cathedral measures almost 8,000 square meters and was declared a World Heritage Site by UNESCO in 1996. (Xinhua/Lu Yang)

Photo taken on Jan. 4, 2019 shows a general view of the Cologne Cathedral in Cologne, Germany. Construction of Cologne Cathedral began in 1248 and was eventually completed in 1880. The total area of the Cathedral measures almost 8,000 square meters and was declared a World Heritage Site by UNESCO in 1996. (Xinhua/Lu Yang)

Photo taken on Jan. 4, 2019 shows a view of the Cologne Cathedral in Cologne, Germany. Construction of Cologne Cathedral began in 1248 and was eventually completed in 1880. The total area of the Cathedral measures almost 8,000 square meters and was declared a World Heritage Site by UNESCO in 1996. (Xinhua/Lu Yang)

Photo taken on Jan. 4, 2019 shows a view of the Cologne Cathedral in Cologne, Germany. Construction of Cologne Cathedral began in 1248 and was eventually completed in 1880. The total area of the Cathedral measures almost 8,000 square meters and was declared a World Heritage Site by UNESCO in 1996. (Xinhua/Lu Yang)

People walk on the Hohenzollern Bridge above Rhine River while the Cologne Cathedral is in sight in Cologne, Germany, Jan. 4, 2019. Construction of Cologne Cathedral began in 1248 and was eventually completed in 1880. The total area of the Cathedral measures almost 8,000 square meters and was declared a World Heritage Site by UNESCO in 1996. (Xinhua/Lu Yang)

Photo taken on Jan. 4, 2019 shows a view of the Cologne Cathedral (L) and Hohenzollern Bridge in Cologne, Germany. Construction of Cologne Cathedral began in 1248 and was eventually completed in 1880. The total area of the Cathedral measures almost 8,000 square meters and was declared a World Heritage Site by UNESCO in 1996. (Xinhua/Lu Yang)

Photo taken on Jan. 4, 2019 shows a view of the Cologne Cathedral in Cologne, Germany. Construction of Cologne Cathedral began in 1248 and was eventually completed in 1880. The total area of the Cathedral measures almost 8,000 square meters and was declared a World Heritage Site by UNESCO in 1996. (Xinhua/Lu Yang)