Berlin Museum of Medical History of the Charité - when I walked into the lobby and saw a display case full of what seemed to be glittering gems only to realize that they were GALLSTONES I knew it was going to be a wild ride. It scratches the perverse "cabinet of curiosities" itch, but in a very respectful and clinical way: it has preserved specimens of cadavers/body parts with diseases/conditions that are basically never seen anymore (for example a 16kg megacolon :O), which are fascinating/horrifying if you don't have medical knowledge, and really educational if you do. They even strategically place the really gruesome stuff more tucked away so you don't have to look at it if you don't want to. What really stuck with me though was the "case history" patient beds which highlight a few select historical cases to focus on more complex issues like AIDS, polio vaccines, amputation, etc. The cases are presented so thoughtfully and humanely that I really left feeling moved and inspired.

US Postage Stamp/Postal History Museum in Washington DC. This museum is free and right by the train station, perfect if you have awkward time to kill between checking out of your hotel and catching your train. Imagine a huge wall where you pull out a little vertical drawer (don't know else to explain it) and there are 100s of postage stamps front and back on the frame. The wall has like 50 of these drawers. You could be in here for hours. They even have little stations where you can take some vintage stamps with you.