We spent over 5 hours in the Prado about 2 weeks ago. Had advance tickets - quick entry. Long line for tickets. Guides offering services near entry. They asked how much time you had and what was of interest. We encountered plenty of guided groups inside. As far as we could tell, the guides knew their stuff. Some moved fast; others very slowly. Indeed, one group was in front of the Bosch "Garden..." for over 15 minutes, describing in painful detail things requiring a telescope to see. Better to read an art book beforehand. We used RS plus our own knowledge and interests for our guide. LOTS of people. But, what a museum! Cafe good & reasonable. Heat and humidity limited our stay, so we came back for the free time a day later. Fuggedaboutit! Longer lines and student groups. Worth a try, I guess. Purchased the Paseo del Arte pass online. Thyssen better than we expected. - spent almost 3 hours. Sofia - Guernica and some Dalis in adjacent room - about an hour. We were not "into" most of their exhibits.