Italy-Sicily-Malta-Greece

Personally for me three weeks would not be enough time to fit in all four destinations. I spent three weeks alone just going around Sicily and just got back from spending 16 days in only northern Italy. Will this be your first trip to Italy or Greece? Lots to see and do in each country and you would need to prioritize destinations just to visit those two, let alone all four of your desired places. If you spent three nights in each of your five planned Italian cities you are already at 15 nights with just six left for Greece. And I would think that you would want at least two to four days of siteseeing in each of these beautiful places. Remember that two nights gives you one full day of siteseeing in a given area and that transportation between cities also eats up chunks of your time. Italy is a big country and you are planning to go from north to south, covering a lot of territory. I think a lot of us here on the forum will recommend slowing the pace and narrowing the scope of the trip. I know you want to see as much as possible but the pace you would need to visit three or four of these places would be draining and you would end up spending most of your time in transit from place to place and not getting much time to enjoy seeing the sites and countryside.

Great blog name.

Sorry to sound like a scold, but you already have 3 countries on your list ; and you want to add more? Really bad idea for a number of reasons. For one thing, the transportation may not be as straightforward as it appears on a map. For another, you are planning to visit one of the sight-richest regions on earth. 3 weeks would be adequate for Sicily or for a trip just to mainland Italy. Of course, it depends on your definition of “see.” Maybe you should check out some big bus tours.

We did Segovia, Madrid, Barcelona, Paris, Belgium, and Amsterdam in 20 days (that included travel days!) and it was wonderful. Is this type of trip completely different?

Yes, this is very different.

First, Segovia (a one-day destination for most people), Madrid, Barcelona, Paris and Amsterdam are all cities; Belgium is a small country. Italy and Greece are large countries, Sicily is effectively a country and Malta is a country, though very small.

Second, transportation within Greece is nothing like transportation in Spain, France and the Benelux countries. There are few express trains; you'll need some combination of slow trains, buses, ferries and flights to get around Greece, plus perhaps a rental car for some destinations.

Sicily also lacks fast trains. It has a lot of worthwhile sights scattered all over. I normally recommend at least two weeks there for folks planning to rent a car for part of the trip; otherwise, it really needs more time than that.

There are fast trains between Venice, Florence, Rome and Naples, but the Amalfi Coast is a lot more challenging. I wouldn't want to add Greece to that list of Italian destinations. Instead, I'd recommend including one of the Italian lakes or somewhere like Tuscany.

Three months would be good for this plan. With three weeks, Sicily + Malta would be good. You will not run out of things to do even if you stick to mainland Italy.
On your other trip, you were zipping along a train line between cities, but once you start inserting ferry rides and flights, it gets complicated--needlessly, since there is plenty to keep you busy in Italy.

sure it's doable, if you like to hit a city/town for a day then move on. i have traveled extensively in the italian mainland, sicily and spent 4 days in malta. i have no experience with greece.

in sicily you can spend a day each in palermo, ortiga, and everyones favorite, taormina. in malta you could spend a day in valetta and perhaps a 2nd day visiting gozo.

and there you have it, both sicily and malta in 4 to 5 days out of your 3 weeks. mind you, it really depends on your travel style. there is no one way.

You need three weeks just to see the key places in Italy.

First, do the big three, Venice, Florence and Rome. Consider adding Pisa, Lucca, Siena and especially the Naples area (Naples, Pompeii, Sorrento, Capri and the Amalfi Coast).
You need 5-7 days just to do Rome properly, 4 for Florence and 3 for Venice. Add the other places and you have little left over.

Greece, the Athens area is a key, including day trips to Delphi, the Temple of Sounion, Corinth and its canal, perhaps the one day three small island tour from Piraeus. Then, you have many great Greek Islands that are best done on a cruise. Islands like Corfu, Crete, Mykonos, Santorini, Rhodes and more.

We spent 21 days in N Italy. We got to Milan, Ravenna, Padua, Torino, Pisa, Siena, and Florence. I have no idea how you could do Italy and Greece in 3 weeks, much less add 2 more countries.

Note that we did not get to either Rome nor Venice. This was quite deliberate. We are not interested in living out of the suitcase.

If you want actual advice, show your planned itinerary, including nights in specific cities.

Your style of travel is not what most here suggest. So you won't get much helpful advice. When I think of your trip, all I see is airports.