In the morning we checked out of the hotel at 11:00 and then killed time until our train left at 14:00. We bought some food and took it to the big park, Mittlerer Schlossgarten, next to the train station to eat.
The Flix train was delayed just like the Flix buses are always delayed. Once we finally left about 45 minutes late, the trip was okay and the train wasn't overly packed as we expected. We had reserved seats with no one next to us so that was nice.
In Frankfurt, the train stopped at the south train station so we had to take the S train to the Hauptbahnhof and walk a few blocks to our hotel. The hotel turned out to be in the worst part of Frankfurt even though it was a nice and modern hotel.
In the evening we went to an excellent Vietnamese restaurant called Sapôres Sàigòn Street Food which was excellent. It is located at Map Location: 50.107929, 8.665877 on the main street to the Central Train Station.