At the beginning of August both my sisters and I visited Prague because we wanted to see for ourselves if it really was as beautiful as people (that I've asked) say. And yes, it really is quite an amazing city. You will see lots and lots of buildings that you won't see anywhere here in Germany. The people are also very friendly and the food is just soooooo good. I fell in love with their local dish called svickova that the lady from the hostel that we were staying in recommended to us. It's basically dumplings with meat and a special kinda sweet cream sauce. Love it! The beer there is also very famous so we tried a few...every day...but! The good thing about the beer is that the taste isn't as strong and bitter as it usually is, which led to us not having such a hard time drinking it. I think that the dark beer was slightly tastier. But that's just me.
Prague has a lot of museums to offer and I would highly recommend the Kafka museum even if you are not a "fan". I am not either but you get quite some insight into his life and his inspirations to writing his books.
We stayed for three days I believe and in my opinion three days are enough to see most of the tourist stuff in Prague. All in all I really enjoyed the trip but if you have to choose between a train and a plane be wise and choose to fly! Even if it's more expensive!