If the flights work out, I fly into Frankfurt and leave three days later. I plan to take a train to Trier (through Koblenz), then rent a car in Trier. I plan to spend a full day in Trier and Saarburg, with possible visits to Orscholz and Burg Eltz. What else should I not miss?

I will return the car to Frankfurt at the airport? Good idea? Or should I return it to Trier and take the train back? I figure I could stay close to the airport (Mainz?) and get there by 8 AM. Any budget lodging (private home) suggestions?

Also, any lodging, attraction, dining suggestions are welcome for Trier and Saarburg, too.

Thank you.