Crossing the Slănicului Valley, a tributary of Buzău, we can admire numerous natural objectives with impressive shapes and sizes, often shrouded in legends. After about 50 km from the entrance on the E20 road, on the asphalted county road that goes up to Slănic, we arrive at the Mânzălești commune. Here, the road passes from the left to the right of the water, and at the confluence of the river Jghiab and Slănicul, a white-gray-green pyramidal block can be seen in the middle of the bed, called "Grunj" or the white stone. It consists of tectonic deposits, mainly a thick layer of greenish-white Dacian tuff between layers of almost vertical marls and sandstones.
These formations are visible both in the minor bed and on the left side of the valley, where they create a landscape distinctive in color and steep slope. The rock, almost 18 m high and with a basal diameter of about 15 m, shows traces of water erosion, highlighted by several steps. Although the minor bed of Slănic is to the left of Grunj, during floods, the rising waters reach its base, causing erosion.
Grunjul is a point of interest both for geological studies and for its special landscape, which is why it is declared a geological reserve.
Source: Parks and nature reserves from Romania, Gheorghe Mohan, Aurel Ardelean, Victor Bortaș ed. Victor B. Victor, 2006
