Most of the European sites are located an hour or more by bus away from the cruise port. How do you cruise to the Alps?
I see this misconception a lot. This simply isn't true in the Mediterranean, with the exception of a few cities, like Rome or Florence. But if you start or end your cruise in Rome, that isn't an issue. Nearly every place we ported in the Med was a short
walk or drive from the port. Even in Athens, it's 20 minutes from the port to the Parthenon. Many of the stops are islands anyway - so you are getting on a boat or plane just to move between them.
Sure, the Alps aren't going to be a good option from a cruise, but it was a fantastic way to see the Med. While other people are catching ferries, packing and unpacking from hotel to hotel, we were sleeping or relaxing, waking up each morning in a fantastic new place It remains the best vacation we have taken to date, with the perfect mix of relaxation, art, history, and even plenty of time to try local food.
I hear cruising Norway is fantastic too.
Traveling Europe by land has it's place and benefits for sure, particularly because you are right that you only get a taste of each location cruising. But even there, how many days are people spending in most cities? When we did Europe by land, it was two days max, so still only a taste. Sure, I would love to spend more time in one location in Europe in the future, but not until I have done enough of it to know where I want to vacation for an extended period (Rome and the Amalfi coast are at the top of the list right now).
With a few days in a great city before a cruise, you can get a little bit of both. We spent four full days in Rome first and had fantastic dinners and late-evening strolls. It was absolutely amazing, but so was boarding the cruise, knowing it was easy sailing from there on. I highly recommend it.
Edit: We liked it so much, that we booked a cruise from Barcelona for next summer so we can see the other side of the Med and even hit up Sicily and the Amalfi coast a second time. We can't wait. We have several days in Barcelona prior to departure too.