The 2.5 km long Krupa river originates southeast of Semič in the village of Krupa. The the river water source is located under the karst river valley, where a 30-meter high natural wall rises above it. The entire riverbank is a natural monument and a Natura 2000 protected area.

The karst natural environment of river Krupa was formed over millions of years, and some endemic species have also settled there. Due to their extraordinary adaptability, they have survived until today. One of the most interesting is definitely Jalžić's congeria, a small freshwater shell that is considered a living fossil. A visit to the Semič Museum House will reveal more about this endemic species.

According to many visitors, the greatest charm of the Krupa River is its quiet and charming location, the picturesque surroundings and a pleasant atmosphere for afternoon walks or picnics.