Gujo is famous for it pure water. The limestone layer surrounding the city of Gujo provide its pure water. Otaki Cavern is a huge cave created on one of those limestone layers by water. The stalactite takes 100 years to grow only 1cm. In this cave, you can see its activity of growing.
There are gift shops and restaurants which offers great local foods and products of Gujo.
The official website: http://www13.ocn.ne.jp/%7Eootaki/ootakicavegate.htm