31 Building, Office skyscraper in Jongno-gu, Seoul, South Korea.

The 31 Building is an office skyscraper in Seoul's Jongno-gu district with 31 floors rising approximately 110 meters. Its design follows the functional lines of International Style architecture, defined by clean facades and straightforward form.

Built in 1970 under architect Kim Chung-up's direction, this structure was Seoul's tallest building until 1979 when the Lotte Hotel was completed. Its construction represented an important moment in Seoul's transformation into a modern metropolis.

The name Samil means "March 1st," after the 1919 independence movement, and the building is also called 31 Building for its 31 floors. Its top floor holds a sky lounge, buffet and restaurants where visitors can look out over the changing city. The building appears at the start and end of the 1971 film Woman of Fire.

The structure sits near Cheonggyecheon Street in central Seoul and is accessible by public transit. Renovations completed in 2020 updated the building's systems while preserving its architectural identity.

Architect Kim Chung-up modelled the tower on Mies van der Rohe's Seagram Building, yet according to the sources he was never paid a design fee for it. The building was sold by the struggling Sammi Group to Korea Development Bank in 1985, and the bank resold it in 2001 for 50.2 billion won to a Hong Kong-registered investment company.