It is popular for sports fixtures and hosts several annual events including a free opera concert at the opening of the opera season, other open-air concerts, carnival and Labour Day celebrations, and the Copenhagen Historic Grand Prix, a race for antique cars. A historical green space in the northeastern part of the city is Kastellet, a well-preserved Renaissance citadel that now serves mainly as a park. Another popular park is the Frederiksberg Gardens, a 32-hectare romantic landscape park. It houses a colony of tame grey herons and other waterfowl. The park offers views of the elephants and the elephant house designed by world-famous British architect Norman Foster of the adjacent Copenhagen Zoo. Langelinie, a park and promenade along the inner Øresund coast, is home to one of Copenhagen's most-visited tourist attractions, the Little Mermaid statue.