I have visited these unique cities 20 days ago. All of these are easy to travel to with the train what I used. Frankfurt in Germany with it's skyscrapers was a contrast to my home town. It was a quiete opposite to Brügge as well, that is a preserved middle age city with Charme. I loved Gent with it channels as well, I should had to paddle my kayak there.. and Amsterdam, it always worth a visit there, especially when the tulips are colorful in Keukenhof