This morning we left the Main River and entered the Rhine. The Rhine is much busier than the other rivers we have been on. There is a great deal of both commercial and tourist traffic. We spent the morning cruising through the Middle Rhine Valley which has castles dotted above each side of the river. They are in various states of repair, some barely still sanding and some in very good shape. We docked in Koblenz around noon. After lunch went toured Marksburg Castle. It was built in 1117 and is still totally intact. It again had endless steps so our legs are getting in shape. We stay here in Koblenz until 4:00AM so we plan to go out and walk around the city after dinner.