On the boat you can reserve guided tours of various complexity for the different port calls, but so far it seems that just getting off the boat and finding transport of your own is a lot less expensive and perhaps a lot more flexible than going with the pre-planned thing. Of course, it's easy with the ship-planned excursions, no shopping around to do, and usually you start off really early to maximize your visiting time. But we like the idea of just free-Wheeling* it. A tour guide droning on and on at some boring building when you really wanted to spend time strolling down the side Streets is not always fun.
It's not as if there are not options of all sorts in port. Au contraire, there's everything from hoofing it with a local map, renting bikes, or getting a taxi, to full-blown tours without the middleman. There are whole villages set up to sell you tours and souvenirs and lunch and whatever. No worries there.
Katakolon, on the Greek Mainland (I checked the map; it is attached), is our big cultural stop of the cruise. The attraction is Ancient Olympus, where the first Olympic games were held. The site is about half an hour by bus from the port, and busses go back & forth every few minutes. So we just get one We are supposed to go back on the same bus, which will get us back to the village with just time to shop before the last ferries back to the ship, but I think you could negociate to take pretty much any bus back, as long as it's with the same company.
The site is huge, and we don't have all day so we just see the outside parts. Perhaps in the museum where they have all the smaller artefacts laid out, there's plenty of explanation about what you're looking at. In the field you just walk around (though do keep to the ground, they will come yell at you for degrading the ruins if you climb on them) with your guide and listen to the commentary.
When we got off the bus, we were in a parking lot full of busses and most of the busses didn't even have room to stay parked there, but dropped off their passengers and went elsewhere. Hordes of people. I was worried that the whole place would be overrun with tourists. We may have been many hundreds, but the place is so large (and we didn't even see all of it, for lack of time) there's room to spread out. Plus, people tended to pass by in guided waves, leaving unpopulated lulls where you could have a corner to yourself for a while.
With some patience, you can even get some nice photos with only limited numbers of strangers in them. At this particular spot people were politely taking turns at the unobstructed view, then going on without walking through the next person's shot. Everybody smiling and nodding, and 'After you, please'. Until a big tour group came along, of course.
Nice countryside. Should stick around and visit it next time. Just taking the bus from the port to the ruins and back, you can see that you're skipping over the real Greece where regular Greeks live and work.
Finally back to the port. There's one side with tiny fishing boats, and one side with colorful pleasure boats for just tooling around in. No big yachts here. Off to the right, however, is boat enough to hold all of these in the hold. Two cruise ships are anchored a few hundred yards out, and the shuttle activity is rocking. Just one of them is enough to fill every chair at the array of waterside cafés - so much for a local beer before boarding and going on our ponderous way.
*oh those random capitals again!