Another use of 5 centimes stamps, in this case a block of four. These are unusual because clerks usually sold stamps in horizontal strips. Seeing a block indicates the sender probably bought a sheet of stamps at the post office.

25 January 1866 Zürich to Zürzach.
The letter weighs 12gms, therefore, 20 centimes. Under 10gms was the standard letter rate of 10 centimes.