This one comes to mind. It was quite expensive and Uma Thurman's father was involved when I used to get the catalogs 20 years ago. They have private and custom tours available.
www.nomadicexpeditions.com
Some others.
www.nomadicexpeditions.com
www.geoex.com - Digging the 22 day train trip through the Silk Road for $50k
Some others. www.nomadicexpeditions.com www.geoex.com - Digging the 22 day train trip through the Silk Road for $50k
How about around the work via private jet? https://www.smithsonianjourneys.org/tours/around-world-priva...