Kirmir Stream which is one of the most important branches of Sakarya River is located near the Gudul County and at the ridges of Koroglu Mountains. The stream which crosses deep meanders between the rocky places forms a valley which is approximately 40 km.

The four-storey and 40 m high cave system which is located at the Yesiloz Village where the stream passes is a place of interest especially for the trekking.