See if you can get a large wall map of the USA locally. That should show you a lot. A little screen just can't give that sort of detail.

You could easily fill three weeks in an interesting and scenic route from NYC. However, if NYC is not the highest on your priority, then check out flying into and out of Denver/ Las Vegas/ Los Angeles/Phoenix or San Francisco.

All these cities would give you access to some of the most spectacular scenery on the planet. However, cities in the east of the country are also well situated to make for a three week scenic and historical loop trip.

I guess I just don't know anything about US
Alternatively, if it is possible, would be to forget about this year and plan a trip for sometime next year, when you have had time to read most of this website and many of the forums. Then you will go knowing just what interests you most and where you wish to go.

Having said that, my first trip I did not know anything either. I just went, hit the road and admired everything I saw and every destination. But then, I had much more time, and very good maps.

If you can't get a good map, such as the National Geographics Wall Map, locally, may I suggest that even at this late stage you purchase a Rand McNally road atlas from the RTA store via the link at the bottom of this page. If you order it now, you will have it in a couple of weeks. It is invaluable, and will show you exactly what is where and all the routes between them. Including scenic routes.

Lifey