I didn't really know what to expect from Potsdam, but it definitely exceeded my expectations. Before going, I read that you only needed about 5 hours, including transportation, for Potsdam, but we ended up spending all day there. We only went inside one of the castles, but it was incredible. There is a whole room decorated out of sea shells! Mike said it was one of the coolest things he'd ever seen, and I think we all agreed.
After our tour of the castle, we walked by the other (smaller) one on our way to lunch. The town of Potsdam is small and cute and has a walking street with lots of shops to look at.
We caught the train back to Berlin around mid-afternoon and were back by the early evening. We did some souvenir shopping and wandering around before calling it a night! I'm sure Mike and I will be back to Potsdam with other visitors, or maybe just on our own, because it was such a great day trip from Berlin with a lot more to offer than we expected.