Udayagiri Fort is one of the most prominent tourist stopovers in the city. Also known as De Lannoy’s Fort or Dillani Kottai, it is a remnant of the regime of Travancore. The fort is surrounded by an isolated hill about 260 high and was used as a training ground for the king’s army. Remains of the furnace used for making ammunition stand as a testimony to the fact. Interestingly, it is said that a brass gun, 16-ft-long, was found in the fort complex but could not be moved even a few feet by a number of people including 16 elephants. Now, the fort has been turned into a natural park and one can find a tree house, herbal gardens, bird and deer enclosures and an aquarium.

The fort was constructed with mud during the reign of the Venadu king, Sri Vira Ravivarma (1595-1607 AD), and later reconstructed with stone during the rule of Marthandavarma (1729-1758 AD). Donations were given by the Nattars of Nanjilnadu to construct the structure. The fort also served as a cantonment under Dutch captain, Delonnoy, who was captured as a prisoner of war by Marthandavarma and later appointed as commander-in-chief of the military equipment, including cannons that were once stored here. Within the fort complex are located a foundry to manufacture guns, cannonballs, mortars. The fort also served as a jail when the soldiers of Tipu Sultan’s army were kept here towards the end of 18th century AD.