Sounds like your girlfriend did the typical North American thing of visiting "Europe" by hitting a bunch of major cities and sticking to the touristy centres.

• The Netherlands is gorgeous, quiet, and safe, but if you don't wander further than one or two kilometres from Amsterdam Centraal, you'll never see that. Rent a bike and ride through Haarlem or Utrecht if you want a proper experience.
• Brussels has some of the best food I've ever tasted, but you have to break away from the tourist traps first.
• Athens is an exciting, "young" city with ancient treasures literally on display in the subway stations. You'll never see that if you just wander around the Parthenon. The food everywhere is great too, though the best spots are usually well outside the touristy areas.
• Paris has some really exciting stuff happening with cycling right now, and the view from Momatre is amazeballs. Yes, the locals can be rude, but fuck it, take the train and get out of the city!

Which brings me to the other important point: Europe is not just the (impressive) cities, but rather a continental patchwork of interconnected but distinct cultures. Have breakfast in a B&B in Arras before you trek out to see the Vimy memorial, then board a train and be in Nyon by dinnertime where you can sit on a clear blue lake and munch on baguette. Hop on the train again and you're in Torino, Venice, or Florence which is just gorgeous. I had the best pizza in my life there in a dodgy little place at 1am.

Stay a few nights in Warsaw and take a stroll through the old city. Gobble some perogi in Krakow and then push yourself to visit Auschwitz. Then take the train across the now undefended border to Berlin where you can walk the path of the former wall, and the next night go for the best danishes in the world... in Denmark.

Seriously, your girlfriend is out to lunch if that's her impression of "Europe". You two need to take another trip and rethink your priorities.