Shinjuku Monolith Building, Commercial skyscraper in Nishi-Shinjuku, Japan.

The Shinjuku Monolith Building is a 123-metre office tower at the edge of the Nishi-Shinjuku business district, with 30 floors above ground and three basement levels. Completed on 30 June 1990, it has a metallic black exterior and stands on a site of 7,167 square metres, with a building footprint of 5,716 square metres.

Completed on 30 June 1990, the tower was built on land owned by the Tokyo Metropolitan Government, which chose construction over sale during the bubble economy to avoid pushing land prices higher. It was the first Japanese municipality to use a land trust, entrusting the building to Yasuda, Mitsubishi and Sumitomo trust banks for rental income. When the 20-year contract ended in 2010, Mizuho Trust alone extended it for five years.

The building reflects how Japanese architects approach modern office design, merging clean geometric forms with functional workspaces in a dense urban setting. It shows how Tokyo's business sector uses vertical construction to create multiple levels of shared services and commercial activity.

The building stands in the Nishi-Shinjuku high-rise district, a five-minute walk from Shinjuku Station's west exit and five minutes from Tochomae Station on the Toei Oedo Line. The 30 above-ground floors are served by separate low-rise and high-rise elevator banks, plus emergency lifts running from basement 3 to floor 30.

The glass facades create changing reflections throughout the day as light conditions shift, giving the building a dynamic appearance. These optical effects make the structure look different depending on the time of day and weather.