On our second day we visited the Museum of Communism (which was very interesting) and then headed off on a three and a half hour walking tour of Prague. Our guide was great but we forgot to tip her (sorry!).
In the evening we headed off to the opera house. There we found that the opera we thought we were seeing (a version of Midsummer Nights Dream by Shakespeare with music by Mendelssohn) was in fact a ballet - modern ballet to be exact. In any case, it was very good, we had fantastic seats and it was cheap as chips. But, I'm glad we read the program (which was also in English) beforehand because it explained the story. Otherwise, it would have been quite confusing.