We found a recommendation for Athens Walking Tours by exploring visitor comments on Trip Advisor.  What a great recommendation that turned out to be.  We had the pleasure of being introduced to Athens by our guide, Vicky Krikki, who was not only knowledgeable, but also extremely personable.  Our walking tour of the major attractions (including the Acropolis) was just what two  'newcomers' needed to then explore Athens on their own.   Our experience was so pleasurable that we attempted to book another tour the following day but unfortunately there was insufficient subscription for a group tour.  On our next trip to Athens, we will certainly start with Athens Walking Tours.  (Don't miss the new Acropolis Museum.)