I do not usually like War Films, but somehow "Das Boot" is the exception, along with other Submarine films, like "Crimson Tide" and "Hunt for Red October".
I had the opportunity to go in a Submarine last summer. Getting in and out was not easy, a ten foot or so ladder with big gaps between the rungs. It was very much smaller inside than I thought it would be. The hatches, or doors are very very small, and the bunks were very narrow, and short. Getting out was even worse than getting in, the ladder was very wobbly and had some rungs missing.
This was at the Maritime Museum in Goteborg, Sweden. (Health and Safety in this Country would not have allowed people on the Sub.) There was also a Gun Ship, and lots and lots of other boats etc. An excellent Museum.