While we were in Rome last June, we tried to get into the Vatican Museums without a reservation. It was late afternoon (after 3 p.m.) but the line was several hours long. We almost got back to the metro station but then my wife found a discreet sign at one of the restaurants by the Walls advertising tickets to the museums. We got them for a little more (some 30%) and we were able not only to skip the line, but even to bypass the line for the people who had pre-reservation. I am not sure if the place was the Trattoria Da Paolo or another place on Vialle Vaticano, but I am at loss why nobody in this forum ever mention this reasonable option.