A girl enjoys herself during the balloon festival at Rheinaue leisure park in Bonn, Germany, on June 8, 2019. The four-day festival, which kicked off on June 7, attracted more than 30 ballon teams from Germany, Belgium and the Netherlands. [Photo/Xinhua]

People look at a hot air ballon during the balloon festival at Rheinaue leisure park in Bonn, Germany, on June 8, 2019. [Photo/Xinhua]

People visit the balloon festival at Rheinaue leisure park in Bonn, Germany, on June 8, 2019. [Photo/Xinhua]

A girl runs in front of a hot air balloon during the balloon festival at Rheinaue leisure park in Bonn, Germany, on June 8, 2019. [Photo/Xinhua]

Two children are seen during the balloon festival at Rheinaue leisure park in Bonn, Germany, on June 8, 2019. [Photo/Xinhua]

People prepare a hot air ballon during the balloon festival at Rheinaue leisure park in Bonn, Germany, on June 8, 2019. [Photo/Xinhua]

People visit the balloon festival at Rheinaue leisure park in Bonn, Germany, on June 8, 2019. [Photo/Xinhua]