Instead of the scheduled overnight stay in Trieste Costa added on Venice as a pleasant surprise.  

One can use the People mover or walk into town. A free shuttle bus from the ship to the people mover is provided by the port. 

Split with the old town and the beach is well worth a visit.  Everything is within walking distance. 

Kotor is a gem that should be included in any cruise in the Adriatic sea.  

Early in the morning the vessel slowly made its way into the end of the fjord in the mist. It was still possible to realise that we'd come to a place of remarkable beauty. Across the street from the pier is the magnificent old town. If you have the physical strength you can walk up the mountain to catch the stunning views. Try to do it as fast as possible, because it gets hot later on. The tenders were very efficient, because Costa had hired a large number of local operators for this purpose. 

Corfu has a lot to offer if you just walk around town. Apart from old fortresses and nice views of the island it's a pretty town in itself. If walking is a problem you can reach the town centre by taxi, bus, horse & carriage or a very expensive shuttle provided by Costa. 

Dubrovnik is as good as they say. The stop in port is short, but long enough to make it over to the Old town which is an absolute must. The taxis are extremely well organised, and the price per car is fixed.