People visit the Paris Opera Theater during the European Heritage Days in Paris, France, Sept. 21, 2019. Historical heritage sites are open to public this weekend in France to mark the European Heritages Days, which are held in September each year. The European Heritages Days are the most widely celebrated participatory cultural event shared by the citizens of Europe. (Xinhua/Gao Jing)

A girl takes selfies at the Paris Opera Theater during the European Heritage Days in Paris, France, Sept. 21, 2019. Historical heritage sites are open to public this weekend in France to mark the European Heritages Days, which are held in September each year. The European Heritages Days are the most widely celebrated participatory cultural event shared by the citizens of Europe. (Xinhua/Gao Jing)

People visit the Paris Opera Theater during the European Heritage Days in Paris, France, Sept. 21, 2019. Historical heritage sites are open to public this weekend in France to mark the European Heritages Days, which are held in September each year. The European Heritages Days are the most widely celebrated participatory cultural event shared by the citizens of Europe. (Xinhua/Gao Jing)

A girl visits Paris Opera Theater during the European Heritage Days in Paris, France, Sept. 21, 2019. Historical heritage sites are open to public this weekend in France to mark the European Heritages Days, which are held in September each year. The European Heritages Days are the most widely celebrated participatory cultural event shared by the citizens of Europe. (Xinhua/Gao Jing)

A girl visits Paris Opera Theater during the European Heritage Days in Paris, France, Sept. 21, 2019. Historical heritage sites are open to public this weekend in France to mark the European Heritages Days, which are held in September each year. The European Heritages Days are the most widely celebrated participatory cultural event shared by the citizens of Europe. (Xinhua/Gao Jing)

People wait in a queue to visit the Paris Opera Theater during the European Heritage Days in Paris, France, Sept. 21, 2019. Historical heritage sites are open to public this weekend in France to mark the European Heritages Days, which are held in September each year. The European Heritages Days are the most widely celebrated participatory cultural event shared by the citizens of Europe. (Xinhua/Gao Jing)