In particular, the relic Nam Giao built of stone located in the arms of the Dun Son mountain range, is about 2.5 km away from the royal citadel to the south.
Nam Giao is of an extremely rare type of relics, is an overall space of a sacrifice stage still intact and oldest of Vietnam. Nam Giao was built in 1402 under the King Ho Han Thuong. This is the place used by Ho dynasty to make ceremonial offerings to Heaven, God, Earth Genie and all of other deities for a peaceful country, peoples safety, national longevity. It had the general characteristics of an Eastern sacrifice stage but also with its own special features of Vietnam, affirmed the very high national pride of Ho dynasty in late XIV and early XV century.
Due to many objective conditions, experienced more than six centuries until 2004, Nam Giao sacrifice stage had been destroyed completely. From 2004, after 4 archaeological excavations, the overall ground of the Nam Giao relic are gradually revealed: that are the base and the overall space of the stage. The traces of the stage architecture are appreared to be running in the north-south direction of 250m, in east-west of 150m with a total area of 35.000m2. From the foot of the Dun mountain, the stage was built up to the five floors, the highest is of 21.7 m above the sea level; the lowest is of 12m higher to the sea level. The main materials to build are green blocks of rock and earthen materials (bricks and tiles..) An architecture has been preserved relatively intact is the Gieng Vua (King Well). The well was built by rock with the square opening getting smaller down to its heart.
The constructions of Ho reign citadel were created by the creative minds of designers and talented hands of the workers at that time. In addition to the event that Ho Quy Ly ordered the prime minister Do Tinh to measure and supervise the constructions, historical documents also recorded the participations of many talented workers used to be served in Ming reign of China including Nguyen An who was involved in the construction of Beijing citadel. The miracle of the citadel short time building is highly evaluated by the experts.