Answer: In Mumbai, the iconic structure that is turned green each year to celebrate St. Patrick's Day is the Gateway of India. The Gateway of India is a monument built during the British Raj in Mumbai and is one of the city's top tourist attractions. The tradition of turning the Gateway of India green began in 2010 and has continued each year to mark St. Patrick's Day, which is celebrated on March 17th. The green illumination of the monument is meant to symbolize the strong bond between India and Ireland.