The Otliško Okno is a unique karst phenomenon and a renowned Slovenian natural monument. “Okno” is a Slovene equivalent for window and bears this name because it has a form of a window, although it is actually a natural hole in a massive stone wall. Moreover, some claim it is a natural stone bridge over this giant hole. This majestic window provides a breathtaking and absolutely stunning view of the Vipava Valley and the nearby village of Otlica got the name after this magnificent work of nature.
The Otliško Okno was formed from a sinkhole by corrosion and erosion just like all the Karst phenomena. Water started to corrode rocks in the sinkhole and spread the fissures in the rocks until the bottom of the sinkhole broke and fell down the slope. The result is the marvellous Otliško Okno, with another, much smaller window just beneath it. From the village of Otlica to the Otliško Okno is a 15 minute walk along a pleasant and narrow terrain.

In 2004, the Stone Spiral, a distinct cultural monument, was built nearby the Otliško Okno by the young architect Damijan Popelar.