I am about to buy a ticket from an Italian city to Frankfurt, and I just noticed that the ticket is much cheaper if I select Stuttgart as final destination.
The flight to Frankfurt is direct, whereas the flight to Stuttgart is via Frankfurt, the first leg on the same flight, and the second leg an a DB train carrying a proper LH flight code.
I believe this is part of the Lufthansa Rail&Fly program, but I am not 100% sure. This should be part of Lufthansa Express Rail, as pointed in an answer below.
My question is the following: can I buy the second ticket for cheaper, and simply stop in Frankfurt? Will Lufthansa notice?
I will be checking a bag (which usually makes hidden city ticketing impossible), but for Rail&Fly Lufthansa clearly specifies that the checked bags are not transferred to the train, it's the passenger's responsibility to do so.