Hi, Kerala has so many wonderful places to be explored :) You can go to Munnar, Thekkady, Alleppey, Kochi, Varkala, Trivandum, Kovalam, Kumarakom, Vagamon! Well, it depends on how many days you have.
You can check these blogs to plan your trip:
Munnar, Thekkady, Allepey, Kochi are the regular touristy places..... If you are opting for some new places means Visit * Athirapally falls * Vagamon * Wayanad * Idukki
If u are a beach person i would suggest kovalam ,and varkala.. if u are a mountain person go for idukki munnar etc... well all these places can be covered in a week.. and yes fort kochi too