Trip to the United States

[Verily]

When you're in Delaware, go to Rehoboth Beach.  In Maryland, go to Little Italy in Baltimore, and the Walters Art Museum.

No. The answer for Delaware is drive through it as fast as possible.

Anyway, the one thing I've heard as advice for Europeans is to be wary of American summers. We don't find extreme humidity followed by sudden torrential rainfall odd, but Europeans generally do.

As my own advice, if you're flying to Washington, stay in the Washington-Baltimore-Richmond-Hampton Roads area. Any further is too much driving for not enough benefit, and you'll be driving more than you'll be seeing anyone or anything. DC by itself is a week-long trip anyway. (Although, if you do plan to go the New York or Philadelphia areas, take the Acela train, and buy a ticket now as they get more expensive closer to the date.)

[Verily]

Philadelphia and Gettysburg, Pennsylvania...where this country was born and saved respectively.

And the beauty of that, is one can drive through the Amish precincts along the way (the horse and buggy folks with hexes on the barns resting on their beautifully manicured organic farms). Sad to say I have not yet been to Lancaster or Gettysburg, but I will do so before exiting this mortal coil, absent lack of notice. Philly  as a town overall is a bit of a dump, but yes has a lot of history, and some of the burb areas are gorgeous.

On a related note, the Amish areas in Ohio are both more picturesque and larger than in Lancaster County. And have been less transformed into a tourist attraction. My aunt lives near there.