We did an excursion in Athens that did exactly that - drop off at Acropolis - pick up near the Plaka. My guess is the locations vary based on parking availability. Your friend may be able to give you a good meeting place. There is a church at one end of the Plaka with a nice public square and a lot of outdoor seating.
All I ask is a tall ship and a star to steer her by; John Masefield
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
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Sail Windjammer: Mandalay 2017
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