Munnar would be an interesting option. The route can go as follows.
From Bodinayakanur in Tamilnadu ( branch line from Madurai), via Munthal-Kottagudi ( along the Kottagudi river ) to 'Top station' at the Kerala-TamilNadu border and further on along the Mattupetty dam reservoir to Munnar. The route can be a meter gauge like the NMR route.
This will be a special route too. About a century ago, the Kundala valley railway used to connect Munnar to Top station with a narrow gauge railway....
more... This was used for transporting Tea to the rest of the country. The tea would be transported from Munnar to Top station by railway. From there, a ropeway and cable car used to take the tea down the hills and by road to Bodinayakanur. The line was washed out in a flood in 1924 and never reconstructed.
The route can be re-started in pretty much with the same alignment as earlier and it will be really good to see a historic route being restarted.