The actress-singer will christen the space (already a well-appointed bar and gathering place called The Granite Room) with her "unplugged" hour-long cabaret performance, to play successive Thursdays in August and September.

Sullivan (of concert halls, recordings, cabarets and Broadway's Gentlemen Prefer Blondes and 3 Penny Opera) will concentrate on the Great American Songbook since the 19th century, with a hint of international music.

Accompanying Sullivan will be pianist Jon Weber, who'll also offer special musical interpretations during pre-show dinner. Doors open at 5:30 PM prior to the 8 PM show. A three-course dinner and show package is $90.

Sullivan's downtown show will play Aug. 20 and 27 and Sept. 3 and 10.

City Hall New York (at 131 Duane Street in the heart of Tribeca) is in a landmark 1863 cast-iron building surrounded by century-old warehouses. Architect Larry Bogdanow and chef/owner Henry Meer created the restaurant. For combined dinner and show reservations, call City Hall Restaurant at (212) 227-7777. Visit CityHallNewYork.com.