oh, you're in Germany that is so cool !
I was just there... last week. (though Germany is about 40 minutes by train from my house, so not that exotic for me).

What part of Germany are you staying in?

For touristy big cities Starsbourg and Nancy are about 2 hours away in opposite directions.
Stras is just amazing, the cathedral and la petite france are must sees. There is also boat tours and Lots of artsy stuff. It's really really tourist based there, so if you don't speak french it's not a problem at all.

Nancy is about 180 km away, it's best know for its style of art l'école de Nancy, or l'art nouveau as the anglophones dubbed it. I was just there this morning, it's les soldes right now meaning everythings 20-70% off, there is some amazing deals to be found (I bought a whole new wardrobe including shoes for under 60 €). There is also la pepinaire , la place stanislas, an aquarium, and several museums made of win.

Smaller destinations include: St Die, geography capital of France (lots of maps), Baccara the crystal capital of France, the adventure park at lac pierre percé near gérardmer (bungee jumping, ropes course, zip line, canoeing etc.). And my personal favourite Lunéville, the castle is beautiful and that's about it, but I went to school there so that makes it cool.

So yeah, your not far away at all, so if you do decide to come up do it before july 9th and I can play tourist guide for you.