The Citadel is often used as a catchall term for Hue's Imperial City, built by Emperor Gia Long beginning in 1804 for the exclusive use of the emperor and his household, much like Beijing's Forbidden City. Most of the site is comprised of crumbling stone buildings and walls overtaken by trees and plants. The natural disrepair gives the place an authentic, ancient feeling. Unfortunately, restoration is happening fast, and inner palaces and buildings are being reconstructed and given a fresh coat of paint. The result is rather kitschy, and a theater toward the north end of the city has been set up for scheduled, somewhat cheesy evening dining and entertainment (250,000 VND per person; tel. 054/352-9857; www.hueworldheritage.org.vn). The city actually encompasses three walled enclosures: the Exterior Enclosure, or Citadel; the Yellow Enclosure, or Imperial City, within that; and, in the very center, the Forbidden Purple City, where the emperor actually lived.
The Citadel is a square 2km (1 1/4-mile) wall, 7m (23 ft.) high and 20m (66 ft.) thick, with 10 gates. Although the complex was constructed by a French military architect, it was actually the French who destroyed it many years later. Get a ticket and enter the main entrance to the Imperial City through the southwest gate, the Ngo Mon, more often called the Noon Gate.
See the Imperial City with a good English-speaking guide. The site is not spectacular in itself, but the history and traditions are rich, and a good guide can give you a breakdown of what things once looked like and what life was like at the Imperial court, and connect you with a dance show of the Imperial Dance Troupe.