London
We spent five days in London, and it's an excellent place for Americans to begin a European journey.  They speak the language (mostly) and the food is pretty familiar, if not cooked beyond recognition.  (For tastier fare, stick to cuisine from former UK colonies, or just drink the beer.)  London is also a great place to begin training for European cathedral-climbing--every town has a cathedral, every cathedral has a tower, and that's what tourists do when they're there.

 We took a day trip to Stonehenge
and then went
On to PARIS!