Amsterdam... one of my favorite cities. Hundreds of great museums, lots of good food, fun bars... everyone speaks English so it’s easy to navigate. Fun place.
Rent a car and drive north on the highway that runs north/south down Italy’s spine. If you’re not in a hurry, you can visit Assisi, Perugia, Firenza, Siena, Vicenza and points north. in addition to the medieval cities, the countryside itself is beautiful. The further north one goes, it gets even better as you approach the Lake District.