Venice’s island historical port is now closed to all but the smallest cruise ships. They now dock at various ports on the mainland; some are as close as 20 minutes while others are 2½ hours away. The prime virtue of the closest ones is their proximity to Venice while the more distant ones have attractions of their own.
The Venice-area ports are busiest in the summer and nearly shut in the winter.
Eastern Mediterranean cruises are most commonly 7 nights long, though they can be much longer if they visit many Greek or Turkish ports.
Combined Eastern and Western Mediterranean cruises can be as short as 12 nights, but 14 or 21 is a more common length and cover more of the sights.
While there is the occasional Trans-Atlantic or Suez Canal repositioning cruise, they are notably fewer than what is available from Rome or Barcelona.