Hello,
There is no train transportation to Munnar,
So its better to get a train to Ernakulam from Trivandrum Central Railway station(Trivandrum railway station 6Km from Trivandrum Airport) From Ernakulam, u can hire any taxi and proceed to Cochin
Cochin- sight seeing, Dutch palace, Jewish synagogue, Fort Kochi Beach, Chinese fishing net etc. Overnight stay.
On another day Move forward to Munnar
A 4 hour scenic drive through hill station. On the way you can visit Valara, Cheeyappara waterfalls, Karadippara view point etc. check in to hotel, Overnight stay
Day 3 Munnar- Sight seeing at Munnar, Visit Mattuppetty dam, Gundala lake, Indo-Swiss project, Eravikulam National park etc. Overnight stay.
Next day Move forward to Thekkady- sight seeing Tea- Cardamom plantations, Boating through Periyar lake, Periyar wildlife sanctuary visit, Spice plantation tour etc. Overnight stay.
On day 5 you can visit Alleppey / Kumarakom- Proceed to Kumarakom , check in to hotel, sight seeing Paddy field, Coconut lagoon, etc. Overnight stay.
On 6th day you can prefer House boat service to Kollam from Alappuza or you can get Train from Alappuza to Kollam.
If interested in Eco tourism sights you can move to Thenmala and spend 1 day there, Its better to hire a taxi to Trivandrum for your return.
Thank you
Have a Nice and safe trip to Kerala
Haris. A