Periyar Wildlife Sanctuary is Southern India's most popular animal sanctuary. It is around a large artificial lake created in 1895, supposedly containing tigers, as well as elephants (certainly).
To be honest, the boat trip around the lake is a waste of time - more like a trip around a boating lake than a wildlife reserve, with overcrowded boats and tourists making more noise than a sports crowd. Much better to hire a local guide and go for an early morning 3 hour walk - you see much more (sometimes too much - see photos of the elephants).
Thanks for your frank appraisal of Periyar. It's what I would expect, and I wouldn't waste time and money on the place. There are better parks in India.