Blautopf
In my opinion the Blautopf in Blaubeuren is one of the most interesting lakes around in the south of Germany. This I think not because of the size (it is tiny), but because nobody has discovered all of the caves accessable through the lake.
Also the colour is amazing. Have a look at the foto. It is not manipulated! The lake is that blue.


Water mill at Blautopf
Hospital of the Holy Spirit
Hospital of the Holy Spirit, chapel
Protestant Parish Church