@ bayern klassisch [#30]

Hello Ralph,
Thanks for confirming the rate. I looked at the back of this and it is very plain with only a Basel transit date stamp and a small circle illegible receiving mark, about 17mm in diameter (probably Frankfurt).

Here is another with the same rating.
17 February 1866 Geneve to Berlin received 19 Feb. Transit Basel, Schweiz uber Baden, and what looks like CH Bad Bahnpost. (I am not familiar with German train marks.)
What does the red crayon indicate? There is a similar red crayon mark on the letter to Frankfurt.