That can get long and tiring if you aren't flying!
There are direct flights but no direct trains for this journey. New Delhi (Delhi) to Port Blair (Andaman And Nicobar Islands) distance is 2479 km and you can get there by flight in just over 4 hours and 30 minutes or by train + flight fares starting from ₹ 4019.
Beautiful weather for sightseeing and other outdoor activity.