A beach is a beach is a beach...... for those of us that do not like salt water or too much sun........

I don't see Japan on the list.
I think Japan is an amazing country, perfect for incredible sights, history, sounds and great food. Impecably clean and organized with tons of options.
Every single airline alliance has many flights to Tokyo or Osaka and every single hotel chain has many options.

Depending on how long they have, a few days in Tokyo, a trip around the country including a stay at an Onsen, down to Kyoto.
It is a very easy country to do things on your own and take some organized tour when there.

Venice

I think if I could go anywhere in the world it would be to one of the many natural wonders of the world that may not be here in 50 years (not creating a debate here) or that are just amazing.

That being said, I think you need to get an idea on what they want to do in order to pick out a great place. Bora Bora, Maldives, Seychelles, Kauai - all are beaches and islands. I would love them but as mentioned a beach is a beach.

Do they like to see the sights, explore natural wonders, just relax? I think the experience of a dream vacation is often more important than the actual place. Of course, most of these wonderful places make the experience. But I think you know what I mean.

Now that I have kids, most of my dream vacations are different from when I was in my 20s and all involve the kids learning while we do. I keep saying "when the kids are older they would enjoy that more."

so they key really is what would they want to do.

Top of my list would be:
China (big country, I know)
India
African Safari
Morocco (cheap, wonderful vacation to be had for all!)
Galapagos
Italy and Slovakia to visit the homelands of my ancestors.
Bora Bora/Maldives/
Cuba
Japan
Egypt
.... list goes on and on

yes, anything sinking would be a good thing to see now while it is still there.

And depending on world politics, one could consider Israel too. I was just there and we also went to Jerusalem. Things were stable.

Whether into religion or just history, or just seeing something very cool, this is a great place to go because of all three reasons!

I have a trip report on the site shown in my sig line

Also wanted to mention that although it is the hip thing to do on Maui, the road to Hana the not-so-legal way is an amazing experience for those who like that sort of thing. Again, not something I can do with a 1 and 5 year old our next trip in April, but it is fun to go the road less traveled on a now more traveled road to hana. Great guidebooks for the more hard to reach sites on the way to hana.