Thanks for everyone's responses, you've given me a lot to think about.
All the hotels that I've booked, though fairly inexpensive have air conditioning, they're all centrally located so that we can walk primarily rather than take public transport.
@acraven, I think you're right about the seine cruise, it may be a bit too relaxing, we may fall asleep on it. Everyone recommends to get their first glimpse of the Eiffel Tower from trocadero, so we might do that. And maybe have dinner there. Yes, we chose our hotel, so that its within walking distance to Checkpoint Charlie, Brandenburg gate and the Reichstag.i have to look into some of the other museums that you've mentioned especially the former Stasi prison, sounds very interesting.
Which would you recommend visiting the camp at Dachau or Saschenhausen?
@rosalyn, I'm planning on registering for just the dome, is the guided tour at the Reichstag worthwhile?
@ Dick, I've already started my journal, very useful in the planning stages, and I can't wait to write about my first impressions of each city we visit. And that's an awesome idea, using the long train rides to write.
@David, I can't shorten my time in Paris, because that's the one place we're going to do a thorough visit of all the museums. And besides its PARIS! But maybe Vienna, but that was the city we were going to focus more on experiences, the coffee shops, heuriges. And I heard about the free concerts/operas in front of the city hall. I think Salzburg, we will do as a day trip, I don't want the hastle of staying in a different hotel for just 1 night.
If I had to do 2 nights in one of the cities, either Prague or Amsterdam, which would you pick?
Thanks everyone, lots of great ideas.