People sit on steps of the National Gallery in London, Britain, on May 17, 2020. (Photo by Tim Ireland/Xinhua)

People visit the Colonna Palace with face masks in Rome, Italy, May 23, 2020. (Xinhua/Cheng Tingting)

A salesman works at a food stall in the Sants market in Barcelona, Spain, May 8, 2020. (Barcelona City Hall/Handout via Xinhua)

The empty Leidse Square is seen in Amsterdam, the Netherlands, April 23, 2020. (Photo by Sylvia Lederer/Xinhua)