One of the few buildings in the old town to survive the 1667 earthquake, the Sponza Palace was built from 1516 to 1522 as a customs house, and has subsequently been used as a mint, treasury, armoury and bank. Architecturally it's a mixture of styles beginning with an exquisite Renaissance portico resting on six Corinthian columns. The 1st floor has late-Gothic windows and the 2nd-floor windows are in a Renaissance style, with an alcove containing a statue of St Blaise.
Just inside the building, before you enter the cloister, is the Memorial Room of the Defenders of Dubrovnik, a heartbreaking collection of black-and-white photographs of the mainly young men who perished between 1991 and 1995.
The 1st and 2nd floors house the State Archives, a priceless collection of manuscripts dating back nearly 1000 years. Though the archives are not open to the public, copies of the most precious and significant pieces are exhibited in a display on the ground floor. There are some English translations, but the displays aren't particularly interesting.