Luknja Valley, where the river Temenica emerges from underground for the last time before flowing into the Krka, is a great starting point for a wander through the Dolenjska countryside. Notable features of the valley include numerous karst phenomena, rare animal species and varied flora. Interesting sights include the ruins of Luknja Castle, an old hydropower plant, the former grange (castle farm) and a sawmill. Climbing enthusiasts can put their skills to the test on the natural climbing wall.
Luknja is a steephead valley on the western edge of the Krško-Brežice Basin, 1.5 kilometres west of the settlement of Prečna. The eponymous river Prečna that rises at the head of Luknja Valley (actually still the Temenica, but under a different name), has carved a valley more than 70 metres deep and 1,140 metres into the limestone terrain. At its narrowest point, the bottom of the valley is just 20 metres wide.
The Prečna spring is one of the larger karst springs in the basin of the Krka. It is here that the Temenica returns to the surface, having disappeared underground in a sinkhole in Mirna Peč Valley. There are three springs in the steephead valley: a permanent spring below Luknja Castle, an intermittent spring in the smaller, northern valley head, and a spring by Luknja Cave.
Eight karst caves have been explored in the area of the steephead valley. The largest of them, with a length of 307 metres, is Luknja Cave, the entrance to which is opposite the main valley head above the valley of the Prečna/Temenica. It is an important refuge for bats. The other caves in the valley are much smaller, with lengths ranging from just six metres to 28 metres.
Investigations carried out by archaeologist and palaeontologist Franc Osole in the rock shelter by Luknja Cave between 1975 and 1976 and between 1980 and 1981 uncovered remains from the Stone Age. Among the finds were numerous stone tools (scrapers, wedges, drills) dated to 12,580 years ago, with a margin of error of plus or minus 520 years.
Above the Luknja spring stand the ruins of a once-mighty castle built by the knightly Luegger family. A castle mill and sawmill once operated at the source of the Prečna and were later used to generate electricity. A hydropower plant is located here today. The Novo Mesto Angling Society has built a large fish farm below the spring. Members of the Climbing Section of the Novo Mesto Alpine Association have created the Luknja rock climbing area with two separate climbing sectors.