The ruined Manchu fortress of Sangiin Kherem — Sang's Wall — sits on the western edge of the city, a roughly 350-metre square enclosure of earth and brick walls about ten metres high. It was the seat of the Qing amban (governor) for western Mongolia from 1762 until Mongolian revolutionaries stormed and burned it in 1912.
Today the walls still stand and you can walk the perimeter in about 30 minutes. The interior is largely empty, with foundations of the demolished administrative buildings visible in the grass. There is no entry fee. The walk up gives a good view back over the river and the modern city.