Amsterdam - Belgium - Luxembourg in 6 days

Six days seems an incredibly short amount of time to "see" all of those places. At best, you can kind of "sample" them. Personally, I'd cut something out - probably Luxembourg, perhaps because it personally wasn't a favorite (I thought the countryside and the little towns were beautiful, but I didn't find Luxembourg City itself all that charming).

Are you driving? That would make it a lot easier to cover a lot of ground more quickly. Obviously the train system is excellent in this region but still more time consuming on a limited schedule. But if driving you could at least do some half day stops more easily without wasting so much time.

Hard to go wrong with Amsterdam and Bruges, in my opinion, though, just a matter of time.

I don't have a car so driving is not an option for me. The train is all I have. The trip is one month from now so hopefully I can get cheap train tickets till then.

I know 6 days is a very short amount of time to see all of them but perhaps just get "a taste" of each country since I'm only here in Europe for one semester. Initially, I wanted to see Amsterdam, Brussels and Lux city and in that case, 6 days would be enough since there won't be that many things to do and see in Brussels and Lux city. But after some research, I thought that Belgium has a lot more nice places that I can spend time in other than Brussels. I always kind of fall in love with the charm with smaller cities than the big ones. For example, Sevilla > Barcelona or Florence > Roma. So many skipping Brussels wouldn't be something that I'd regret doing.

Well, when you ask people's opinions of cities, you have to take them with a grain of salt, because we all have different views of what is "charming" and what isn't.

Me? I loved Bruges (and nearby Ghent), thought Brussels was OK, and didn't care for Antwerp at all. But you'll find plenty of people who hate Bruges because it can feel like a big tourist trap (especially in the daytime) and love Brussels, Antwerp, or both. And I've found more than one person who loved Luxembourg City a lot more than I did.

If you are going to change trains in Brussels anyway, it might be worth a few hours just to leave your bags at the station and stroll down to the Grand Place and check it out.

If you're going to use trains, I'd go to Bahn.com and plot out the travel times from place to place and just see what makes sense. There may be cases where a bus is quicker and cheaper (though I greatly prefer trains myself). Within Belgium, I'd most definitely take the trains.

You did your research so go with what already struck your attention. It is good to get a taste to see and maybe go back again.

You should fly to Amsterdam there is a direct from Stuttgart (but you have to buy it like now to save money)
and make your way back by train.
Amsterdam 2 nights
Train to Antwerp or Brussels 2 nights (make the decision to take a day trip to Bruges when you get here)
Train to Luxembourg 1 night.

If you have two nights in Belgium, spend the nights in one city and daytrip to the other. For the record, I love Brugge.

Why don’t you focus on zThe Neyhetlands alone? The Hague, Leiden and Delft would be a wonderful trip. Or also go to Brugge. You need two weeks for your itinerary.

A Bruges lover here as well, and we didn't get the tourist-trap thing that's so often thrown at that one. There were plenty of places away from the Burg and Markt that weren't overrun, and fascinating history, art and architecture. Very nice people, too.

We also enjoyed Antwerp and Ghent but you don't have time, really, for more than Amsterdam and maybe a day trip to Ghent or Bruges from one or the other.

I enjoyed Luxembourg City. I found the American Cemetery particularly moving. You can easily access it by local bus and a short walk. It is worth the effort!

If you have 6 nights ...

Day
1. Karlsruhe to Amsterdam (3)
2. Amsterdam
3. Amsterdam
4. Via Antwerp to Ghent (2)
5. Day to Bruges
6. Via Brussels to Luxembourg (1)
7. To Karlsruhe

If you only have five nights, I would drop Luxembourg.

If you are interested in architecture and trying to decide between Antwerp and Bruges, I'd recommend Antwerp. In addition to its spectacular Gothic cathedral, it has one of the most amazing train stations in Europe. The Art Nouveau district in Zurenborg is one of the best preserved neighborhoods of its kind, and the Boerentoren (Farmer's Tower), now the KBC Tower, is an Art Deco masterpiece -- it was once the tallest skyscraper in Europe. Also, if you are a student, you'll find Antwerp to be a younger, more contemporary city than Bruges, which is basically a tourist town frozen in time.

Adding to T., you might prefer sleeping in Ghent to sleeping in Bruges, because Ghent is a university town and there is no night life in Bruges. But I also prefer Antwerp, including for daytripping to Bruges. Ghent might have the cheapest rooms, but Antwerp has plenty of choice. I think you might have gotten cheaper trains farther in advance than one month. Local trains in Belgium are not discounted in advance, and are usually bought the day of travel. Have you checked discount airlines yet?

I also suggest dropping Luxembourg. Why did you pick it? I've been to Luxembourg city, and either Belgium or the Netherlands is a better use of your limited time. Are you already visiting Germany on weekends? Really, Cologne on the way to Antwerp or Amsterdam is a better use of your time than Luxembourg.