Quadrangular Tower, Stone keep in Old City of Baku, Azerbaijan.

The Quadrangular Tower in Baku's Old City is a multi-level stone structure with thick walls originally designed as a military fortification. The building contains several interior chambers and spaces arranged for defensive functions, with ground-level passages connecting it to adjoining structures.

The tower was built in the 15th century, according to Sara Ashurbeyli's reading of A. G. Rahimova's 1971 study. The Shirvanshah court poet Badr Shirvani records that Ghazanfar Shah, brother of Shirvanshah Khalilullah I, had it built in 1428–1429 to strengthen Baku's northern defences. It served as an armory, called cəbbəxana in Azerbaijani.

The tower now functions as a center for traditional crafts and regularly hosts exhibitions where local artisans display and sell their work. Visitors can watch craftspeople at work and interact directly with artists working within the space.

The tower sits within the Old City and is easily reached on foot from the main tourist routes of the area. Wear comfortable shoes since access to different levels involves steep stairs and uneven surfaces throughout the structure.

The tower stands above an underground passage that ran along the inner side of the northern wall as far as the Double Gates, letting soldiers move weapons to the armoury without crossing open ground. Some researchers think a tunnel also linked it to the Shirvanshahs' Palace or the Maiden Tower.