One of the best ways to get around in Europe is obviously by train. But when you have to go long distances, sleeper trains are definitely the way to go in order to maximize your time. Especially when you have a long ride like our 13 hour one from Rome to Heidelberg.
It's great to fall asleep in one country and wake up at your destination in another. Almost like you didn't travel at all. It's not the most comfortable bed I've ever had and it's a cramped room in 2nd class. There are six people sharing a room with three beds stacked on opposite walls. But it is efficient!
We booked all our train rides using our Eurail pass. We'll have to post a travel tip about that one at a later time though.