We stayed for 2 nights in Venice prior to embarking which was an ideal way of preparing for our cruise. We highly recommend the valporetta bus. Buy a day or two day pass and just cruise and see the fantastic sites. The sail out of Venice is one of the highlights.
Santorini -- tender to shore followed by a 30 minute wait for cable car (which was expected and not a problem). My wife enjoyed the cable car, I found it truly terrifying in an earthquake zone, but it is a matter of choice! The bars and restaurants in Santorini were very nice with fantastic views and not that expensive. We walked down which was fun but took some time. They say the sunsets at Santorini are amongst the worlds best and I can confirm they even put the famous Margate sunsets in the shade.
Katakolon. We took the tour to Olympia having attended the recent London games. Tour guide was good and knowledgeable. The site was evocative of games past, the old stadium itself in remarkable good condition. As a treat we listened to the epic 5000 metre recording we made in the Olympic stadium with Mo Farah. On return we spent an enjoyable afternoon at a dockside bar with free wifi, good beer and we met some nice English people who had been on the Thomson Majestic.