A country that keeps its best things in drawers, and will show them to you if you write first.
One entry is an embarrassment, not a verdict. Germany holds more study collections per square mile than anywhere I know, and I have so far written up exactly one of them. The rest is a list, not a directory, and I would rather admit that than pad this page.
The German habit worth learning is the appointment. The best rooms here are working rooms — print cabinets, drawing collections, study reserves — and they are not on the ticket. Write two weeks ahead, in plain German if you can manage it, and be specific about what you want to see.
Mondays close most things. The trains do the rest of the planning for you: nothing in this country is more than a morning from anywhere else, which is why I keep telling myself the other cities can wait, and then they do.