The AATG summer study program is a truly one-of-a-kind experience. It's three weeks of complete immersion: German in school (the Gymnasium), German at home, and German with friends. My stay in Bonn was far better than I had hoped for. My host family was extremely nice, and they showed me real German culture, the kind of everyday culture you won't find at hotels. They took me kayaking on the Rhine and brought me to a cello masterclass (I'm a cellist) at the Beethoven House led by the famous Steven Isserlis!
At school, I experienced a range of classes led in German. That was another avenue for enlightenment, one I wouldn't, and couldn't have experienced without the AATG. There were several excursions, including one to Cologne and one to Burg Eltz. Essentially, I got to do all the tourist-y things in Germany, while still completely immersed in the language and culture.
If that doesn't convince you, then maybe the fact that I was given ample free time to explore the city will. With easy access to public transportation and ten friends, I was able to take in German culture in its most direct form: food. Assortments of sausages, kebabs, and sauerkraut were set forth and promptly consumed. Needless to say, it was amazing.
As an added bonus, my host father noticed I was reading a book about ancient history and took me around Bonn to various Roman ruins, and gave me a book about it at the end of my stay. The program was pretty much the most authentic German experience you can get. It was a boost to my facility in German, but more importantly, further invigorated my spirit for learning German, even back in the States.