I have done this 100s of times. Route 66 is O.K., but drive U.S. 50 from the Eastern Shore of Maryland to Sacramento, CA. It goes through Maryland, Virgina, West Virgina, Ohio, Indiana & Illinios (boring), then Missouri, Kansas (boring), Colorado, Utah, Nevada (the loneliest rosd in America), & California. This is a great drive, take your time, maybe 2 weeks. Enjoy.
www.zagreb-touristinfo.hr/ Begin with Zagreb, Croatia - Old Metropolis in the Heart of Europe