The Old Exchange was built between 1767 and 1771 by South Carolina's provincial government. It served as a custom house, a public market, a meeting place and a jail. In 1774, confiscated tea was stored here.
After the British captured the city in 1780, they used it as a barracks and put prisoners in the basement. A 2012 study documented at least 120 prisoners held there. In 1788 the building hosted the South Carolina convention that voted to ratify the United States Constitution.
It later served as a post office. Wikipedia also notes that enslaved people were sold in front of and north of the building for many years. The building became a National Historic Landmark in 1973 and is now a museum.