Suggestion on what to do in Cephalonia, Greece for the day??

We are going to Cephalonia on the Queen Victoria and we have never been there before.

I was wondering what is their not to miss in Cephalonia?? & what would you recommend doing here for the day??

Any ideas / suggestions are very welcome :)

Following. We are in Sept.

We visited Cephalonia on a cruise with Seabourn 2 years ago and enjoyed our time. However, we docked on the Eastern side of the island (originally Fiskardo but later changed to Sami) and it will take 30-40 minutes to get across the island by car. On the Eastern side near Sami is Melissani Lake which is an underground lake that I would guess is similar to the grottos (Capri, Malta, etc) that exist in other areas of the Med. It was interesting for a 5 minute cab ride from Sami but I'm not sure I would have bothered from Argostoli... There is also the Drogararti Cave which has fantastic stalagmites and stalactite formations. This is also nearby Sami. We toured both in about 2 hours and then wandered around Sami for 30 minutes or so before heading back to the ship. I've been told there are beautiful beaches but we aren't beach people so didn't bother to find them. There are also very old churches/monestaries in the area that are supposed to be interesting but we didn't visit any.

Hope that helps

Thank You very much for the information Spree75 very helpful! :)