This is the classic Kerala triangle: the tea hills of Munnar, the wildlife and spice country of Thekkady, and the backwaters of Alleppey. It starts directly in the hills, so you spend less time in Kochi and more time where Kerala is greenest.
The route runs south and west, and each drive stays under about five hours. You climb to Munnar on the first day, go down to Thekkady on the third, and reach the backwaters on the fourth, finishing with a night on a private houseboat and a last night in Kochi.
If you want a night in Fort Kochi at the start, see our 7 Days Kerala Tour, which adds it.