Columbus Tower, Steel-framed flatiron building in North Beach, San Francisco, US

The Sentinel Building, also known as Columbus Tower, is a seven-story steel-framed structure completed in 1907 at the intersection of Columbus Avenue, Kearny Street, and Jackson Street. Its wedge-shaped plan fills a triangular block, with a green copper facade, rows of rectangular windows, a rounded corner tower topped by a small dome, and red awnings at street level.

Construction began before the 1906 San Francisco earthquake, and damage to the site and the rest of the city slowed the work considerably; the building was completed in 1907. It was designed by the firm Salfield and Kohlberg, named for architects David Salfield and Hermann Kohlberg. Its top floor first housed the headquarters of local political figure Abe Ruef.

The building carries strong connections to cinema, having served as the headquarters for American Zoetrope since its purchase by filmmaker Francis Ford Coppola in 1972. This role shaped how people in the neighborhood view the place and continues to draw those interested in film and creative work.

The building sits at a busy intersection where three neighborhoods meet, making it a good reference point for exploring the surrounding areas. The ground floor has a restaurant where visitors can stop to rest and observe the intersection from inside.

The basement hosted the hungry i, an 83-seat nightclub opened by Eric Nord around 1949–1950 and sold to Enrico Banducci in 1951. From 1953 Banducci booked comedians such as Mort Sahl there, and the venue's success drew queues around the block until it moved to the International Hotel on Jackson Street in 1954.