If you're looking for a cruise, you'll see the option of mini-cruises on various websites. Don't think this means taking a cruise on a tiny ship—not at all. A mini-cruise is a cruise of 3 or 4 days, sometimes up to 5. It's like a taster of what will later become a longer trip.
The most common mini-cruises from Spain depart from the ports of Barcelona and Malaga , and on them you have the opportunity to reach the Balearic Islands, or to explore the French Riviera, including Cannes.
A mini-cruise that I think is well worth considering is the one offered by cruise lines departing from Athens. You can travel to the Greek capital for a very reasonable price and then embark on a 4 or 5-day mini-cruise around the islands and the Eastern Mediterranean for under €400 per person. The 4-day itinerary includes Athens, Milos, Heraklion, Kusadasi, and back to Athens. As I said, this is just one of the options you'll find online or by visiting your travel agency.
These are the mini-cruises by sea, departing from the most common ports, but don't rule out the possibility of river cruises of the same duration that will take you to incredible cities and places, for example, a mini-cruise through Paris and the Normandy Coast, or from Bordeaux through Aquitaine…in short, there are many more possibilities than you think, and keep in mind that these cruises are always done on the same ships as the others, meaning that you have access to all the restaurants, pools, shows…just like any other passenger.
Sometimes these mini-cruises are organized ad hoc, themed for cheese or wine lovers, such as this one organized through Argentina, and experts are invited to share with them during those days.