A han is an Ottoman urban caravanserai, designed to serve the needs of long-distance merchants in a city. Lodging, storage, workshops, and trading offices occupied the same complex, organized around internal courtyards where animals could be stabled and goods unloaded. The Büyük Valide Han is the grandest surviving example in Istanbul. Its main courtyard is approximately 55 meters per side — a substantial open space surrounded by two-storey arcades. On the ground floor: storerooms and animal quarters. On the upper floor: the merchant lodgings, reached by external staircases. Two additional smaller courtyards extend the complex to the east and west. The whole thing is built in the characteristically plain Ottoman commercial style, with none of the decorative elaboration of a mosque or palace. Its power is in its scale. Walking through the main gate into the central courtyard, the size of the enterprise becomes clear — this was not a waystation but a small city of commerce.

The most unexpected feature of the Büyük Valide Han is the small mosque that occupies the center of its main courtyard. It is a Twelver Shi'a (Jafari) mosque, established to serve the large community of Iranian merchants who lodged in the han — one of the most significant Shi'a places of worship in Istanbul. The original structure burned down in 1947 and was rebuilt in 1951. It remains open for Shi'a observances today, though only on certain occasions. The presence of the mosque is a reminder of how cosmopolitan the han's commercial world was: Sunni Ottoman city, Shi'a Iranian mosque, merchants from across the Islamic world and beyond, all conducting business under the same arcades. The waqf system — the pious endowment that financed the complex — tied its revenues to the Çinili Mosque in Üsküdar, making the commercial activity of the han a form of permanent charitable giving.

The site has older stories embedded within it. The northeastern section of the han incorporates the remains of a Byzantine structure known as the Tower of Eirene, a remnant of the city that preceded the Ottoman conquest of 1453. Istanbul is full of such layering: the Byzantine infrastructure absorbed into, built over, or simply continuing to exist beneath Ottoman construction. The han itself stands on a hillside in the Mercan district, a short walk from the Grand Bazaar — not physically inside the covered bazaars, but part of the same commercial ecosystem. The street it faces, Çakmakçılar Yokuşu (Flint-Makers' Hill), was once lined with specialist craftsmen supplying the trade flowing through both the han and the bazaar. Today the workshop tradition persists: coppersmiths and craft ateliers still operate in the upper galleries, and a tea house occupies the central courtyard.

The han was built through the waqf system — Kösem Sultan's endowment meant that the complex's revenues were legally dedicated to maintaining her mosque in Üsküdar for as long as it stood. This mechanism gave Ottoman charitable institutions a kind of permanence: they were not dependent on individual goodwill but on a legal structure. In practice, many hans declined as Ottoman commercial networks shifted and as more modern forms of business accommodation became available. The Büyük Valide Han suffered fires, neglect, and the general attrition of centuries. Of the estimated 210 to 366 rooms and perimeter spaces it once contained, roughly 115 rooms and 40 shops remain active today. What is remarkable is not its decline but its survival. The complex still functions as a working courtyard: workshops occupied, the mosque periodically in use, the tea house open. A building from 1651, in continuous if reduced use, in one of the world's most layered cities.