Son Tay ancient citadel was built in the 3rd year of Minh Mang Dynasty (1822) with unique architecture. It is rated as one of the most famous and beautiful citadels in the North.

The citadel was designed as a quadrangle with an area of about 16 hectares.

 Its walls, about 4.5 m high, were built of laterite, the typical building material of Son Tay. 

The four gates, West, East, South and North, are made of bricks.

According to the bibliography, the citadel was built very solidly with the main task of protecting the northwestern area of Thang Long.

At present, most of the citadel is in ruins.  

The citadel is surrounded by a moat over 25 meters wide, 4 m deep and 1,792 m long, connected to the Tich River.

In the past there were brick bridges spanning the four gates across the moat but only two bridges exist now.

Some works inside the citadels are still preserved, such as the flagpole that is 18 m high, the Kinh Thien palace and two lotus ponds in front of Kinh Thien Palace. Some works have been restored.

Currently, the citadel has only three gates: South, North and West.

The peaceful scenery of the citadel has made it an ideal location for wedding photos.