I just went like last week with no ticket reservation. Me and my family just walked right up and bought tickets to get into the museum right on the spot.
No, I think it depends in how busy they are. I went to the U505 submarine and they let me in without seen my reservation time.
No reservations are required
Not required but definitely get them. It is so so much better to book everything ahead of time. Start with the submarine, that fills up fast and it's a great thing to do first because it is a nice walk through a lot of different areas which you can then swing by on the way out. Second book the coal mine!
They are not mandatory
Reservations are encouraged but not mandatory at this time.
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