two nights away from Berlin

Prague is 5 hours by train from Berlin; Vienna is almost twice that (I flew that stretch on Air Berlin). If you want to see Berlin plus one of these other cities, fly into one and out of the other. To do this, use the "multi city" option on Kayak, Orbitz, etc. Don't book two one-ways, as that's much more expensive. I feel Prague and Vienna each deserve more than 2 days (and I didn't even care for Vienna, but you can't say there's not a lot to see). If you really only have two extra days, a better plan is to fly round trip to Berlin, and spend two days in the middle in a closer city, like Dresden, Hamburg, or Leipzig (each 2 hours or less by train from Berlin). In addition to being closer, these cities are easier to "do" in a short time. To check train times between cities, follow these directions: http://www.ricksteves.com/plan/tips/db_tips.htm, You can also use the Bahn website to book tickets in advance; if you can accept non-refundable and non-changeable tickets, you'll have a substantial saving by doing so. To find flights, use Skyscanner: http://www.skyscanner.com

How about Poznan or Wroclaw in Poland? Easy train ride away...

Hi, Some good suggestions made above but I'll comment on going to Vienna if that ends up as your decision. I would do that by night, tailor your own route. My suggestion to take Berlin-Munich CNL, then the RJ to Vienna, arriving before noon at Westbahnhof. Several big hotels (depending on your price range) are in the immediate area, ie. within walking distance.

Vienna is too far away (by train), Prague would be possible. But 2 nights probably means only 1 1/2 days of seightseeing, which isn't much. You could also visit some small towns (relatively) close to Berlin, which would be a nice contrast to the big, modern metropolis. 3 hours to the West of Berlin are the medieval towns of the Harz mountains, with thousands of half-timbered houses. Two of them, Quedlinburg and Goslar, are World Heritage Sites. 3 hours to the North of Berlin, on the Baltic coast, are the preserved towns of the Hanseatic League (3 of them, Lübeck, Stralsund and Wismar, are World Heritage Sites). And Schwerin offers the Neuschwanstein of the North. And 2 hours to the South is Saxony, with Dresden and many perfectly preserved small towns, like Meissen or Görlitz, a gem with 4.000(!) listed buildings.

Gorlitz is close to Berlin on the border with Poland...fabulous small town. Not super touristy, but stunningly beautiful and cheap!! Great food and you can walk across the bridge to Poland. It's in RS book. You could spend one night there and one in Dresden (about 90 minutes apart if I remember). If you are adding Prague, I'd limit Berlin to 4 days and spend 3 in Prague.