If you're flying, dont forget to keep a good book for company.
There are direct flights and trains for this journey. kolkata (West Bengal) to Thiruvananthapuram (Kerala) distance is 1987 km and you can get there by flight in just over 4 hours and 10 minutes or by train fares starting from ₹ 688.
The heat there will make you sweat, but it's surely bearable.