St Mary's Cathedral is Australia's largest Catholic church and a neo-Gothic masterpiece. Construction began in 1868 and the spires were completed in 2000. It features stunning stained glass windows, intricate mosaic floors covering 1,200 square meters, and a crypt containing the remains of Sydney's archbishops. Located opposite Hyde Park, the cathedral is one of the city's most significant landmarks. Mass is held daily. Visitors should respect dress codes and ongoing services.