Please elaborate (where did you go, what did you do, why was it so great?)
I had to think long and hard about this but it was probably in 2004, a trip to Japan in summer. It was organized by the German Sport Youth Association (I don't know the correct translation) and about 120 young German people were to travel to Japan.
The whole airplane was booked by us and the long flight itself was fun!
We were assigned to two different host families (stayed in two different prefactures) and also had time for ourselves in Kyoto/Osaka and Tokyo. I lucked out, had very nice host families and I got along very well with my group.
And we also participated in many events, learned Japanese pottery, making a doll, dance lessons, sports acitivites, going to the beach, onsen, fireworks...
The weather was perfect for the three weeks!