Some of the best things about Thanjavur:
1. Culture: Thanjavur is actually the core of Tamil culture. Infact Thanjavur and Chola empire form the crux of TN culture today.

2. Irrigation and agriculture: Thanjavur, as mentioned in other answers forms the rice-bowl of Tamil Nadu. The main reason is the amount of fertile soil in the Chola region (alluvial soil which is ideal for rice cultivation) and the tributaries of Kaveri river.

3. Art and architecture: This image speaks for itself:

4. Kumbakonam degree coffee: I guess, you wont put off a trip to Kumbakonam, just 3 -4 hours away from Thanjavur. Famous for its temples and its coffee.

5. Bharatanatyam Dance: If you are a dance lover, then you will surely appreciate the traditional tamil dance played in the Big Temple.

6. Royal Palace: The reisdence of Bhonsle family. Another tourism spot.