I'm doing an overnight to Meteora by train. We will do a tour of the monasteries, and I think a sunset "walk, drive". Is there anything else I shouldn't miss?
If you have time (but I don’t think you will with the brief amount of time you have), there is a Byzantine Church in Kalambaka. Whether or not it will be open due to covid, I don’t know. Your hotel could direct you on how to get there. The church is tiny. When we were there years ago, there was a local lady who gave a “tour” of the church. She didn’t speak English so she pantomimed the frescoed scenes on the walls of the church. It was pretty hysterical and one of our favorite memories of Greece.