The Washington Square Park, a registered historic landmark that is better known by its nickname Bughouse Square (derived from the slang of bughouse referring to mental health facilities), was the most celebrated open air free-speech center in the country as well as a popular Chicago tourist attraction. It is sometimes referred to as simply Washington Square. It was located across Walton Street from Newberry Library at 901 N. Clark Street in the Near North Side community area of Chicago, Illinois, USA. It is Chicago's oldest existing small park. It is one of 4 Chicago Park District parks named after persons surnamed Washington ( Washington Park, Harold Washington Park, Dinah Washington Park). It was added to the National Register of Historic Places on May 20, 1991 and the neighboring Washington Square Historic District was later added to the register August 21, 2003. The Washington Square District was declared a Chicago Landmark on May 16, 1991 and Washington Square District Extension was declared a Chicago Landmark on July 10, 2002. A second extension was declared a Chicago Landmark on May 11, 2005.