I've had nice vacations before, but I don't know if I'd consider any of them dream vacations.
A dream vacation with my family would be to go with my mom to her home country and see the places she used to live and go, meet the family I've only ever talked to on the phone, and basically eat a bunch of food and explore the local culture. I'd like to do the same thing with my dad's country, but he died when I was a kid and wasn't close to his family at all, so I imagine that would be a lot more difficult. Basically, a family oriented dream vacation would be all about trying to see where my ancestors come from and what those countries / cultures / and traditional foods are like, and get more insight on what my parents lives were like before they came to the US.
A dream vacation with my friends would be a cross country road trip. Either by car or by train, I'm happy with both. I haven't spent much time outside of NYC, and I've never been off the East Coast at all, so I'd like to see the country, go to weird museums, check out local culture and activities, and eat different regional foods. I'd really like to see the Pacific Ocean, and San Francisco is a place I've always wanted to visit.
If I were to plan a vacation alone, I'd like to go somewhere like Iceland or Alaska, or Patagonia, or Nepal.. somewhere isolated and remote. I'm not very experienced when it comes to being out in nature and camping and hiking and all that, but I think it would be a nice way to travel alone - to embrace the solitude and nature and kind of push my own physical limits. Get out of the city and my comfort zone and just do something different.