We spent the afternoon of our first day there on a tour of the concentration camp Dachau. This was one of the most unique and memorable things I've ever done and I highly recommend it. You can take the U-bahn out to Dachau and tour it yourself, or you can go with a tour guide like us, which I am so thankful we did.
Our second day in Munich we ventured out to Neuschwanstein castle...! It's a 2 hour train ride from Munich and takes most of the day but is totally worth it! Take the train to the city of Fussen and make sure to book your ticket ahead of time!