Very close to Pandavapura in Mandya District is the Tonnur village which has a large artificial lake constructed by embanking the gorge between two adjacent hillocks. This lake was named Tirumala Sagara after Sri Ramanujacharya, who is believed to have sponsored its design and construction.

Locally, this lake is called as Tonnur kere. The height of the dam is about 230 metres and the length is about 150 metres. It is believed that Sri Ramanujacharya broke open a portion of the hillock with the help of his tridanda or walking stick to aid water outflow.

The outflow of water from the lake emerges through a narrow passage and has created beautiful waterfalls popularly called as Ramanuja Gange or Tonnur Madaga. Visitors can get a beautiful view of the lake from the top of the hillock called Padmagiri.

The water flowing from the channel irrigates a vast stretch of land below the tank. The transparency and clear water in the vast lake present a panoramic view from the bund. The colour is further enhanced when the blue sky and the hillocks are reflected in the vast sheet of water, simmering with sunlight. The beautiful landscape around the tank further highlights the panorama.

Nasir Jung, the Mughal Subedar of Deccan, who visited this place in 1746, described the waters of the lake as Moti Talab meaning The Pearl Lake, signifying the clear white and bluish green pearl colour of the huge spread of water.

Tonnur, also known as Tondanur, is a place of considerable antiquity and historical importance. The village has played a great role in history after the arrival of Sri Ramanujacharya, the great Srivaishnava saint and reformer of 12th century.

The fact that Sri Ramanujacharya, after leaving Srirangam, stayed at Tonnur for several years before finally arriving at Melkote, accounts for it being a centre of pilgrimage. The village is also a place of artistic interest with its many temples and shrines dating back to the times of the Hoysalas.

At present, there are four temples in Tonnur, either constructed or renovated during the period of Hoysala rule. The Lakshminarayana temple, popularly known as Nambi Narayana, is the largest and the oldest temple. The Gajalakshmi panel on the doorway and the lathe-turned and finely polished soapstone pillars in the navaranga are very attractive. The finely sculpted idol of Narayana is enshrined in the sanctum sanctorum.

Nearby is the Krishna temple which is also worth a visit. The beautiful stone swing right in front of the temple is used only on certain special festive occasions. A visit to Tonnur and Moti Talab will be an excellent outing well spent.