Italian's have a passion for SCUBA diving. SCUBAPRO, MARES, CRESSI SUB, COLTRI SUB and other manufacturers of diving equipment are originally Italia companies. The entire coastline of Italy offers some chance to SCUBA dive. The majority of the recreational SCUBA diving to be done in Italy is deeper than 20 meters, and you need to ensure you review all your basic skills and dive safe.
SCUBA Diving in Italy is not like the Caribbean or Red Sea, the depth is deeper, the visibility could be less than 10 meters, and you need a wet suit. This style of diving means you normally only do one or two dives during the day. Which works out great considering you can dive in the morning and then visit Venice in the afternoon.
Wrecks are the main attraction (in my opinion), I have visited over 100 thus far and have another 100+ on the list to do. Some are just scrap piles and require a bit of imagination others are still fully intact and offer plenty to explore. Many of the wrecks are at the limit of Advanced Divers, and it would be best to be skilled in Extended Range or Deep Tech Certified Divers to fully enjoy.
Caves are popular in Italy and many dive area's will take you through trenches and small grotto's. You need to ensure you are properly trained to do any type of dive, in Italy they do not always control cards as closely as in US destinations, so listen to the dive plan and dive within your comfort level.
There are several national parks established and over the past few years with the warming of the water and control of commercial fishing, you can dive and enjoy underwater naturalist.