At the north-western foot Stupeļi Hillfort there is a large memorial stone, length – 6,80 m, width – 4,90 m, height – 2,75 m, circumference – 20,70 m, volume – around 40 m3.There is a small trail leading to it. On the smooth surface of 25 m2 of the stone there is a small natural, flat hollow. This is particularly interesting because a shallow groove is made right next to the stone found in the deepest layers of the soil. On the eastern side of the surface there is a jag from a split-off, due to the effect of fire, it was separated in layers already in ancient times, because these splinters were also found in the lower layers of the cultural layer. The shape of the stone itself somewhat resembles an inverted pyramid, which is made of a special type of granite - viborgite. Archaeologists trying to solve the mystery of the big stone of the Stupeļi Hillfort in the 1980s found that it was probably used in ancient times as a cult stone, where the Selonians performed rituals. Archaeological excavations took place near the stone in 1977-1978, during which various antiques of the 10th–13th centuries, including pottery and bone fragments, probably, for the purpose of offerings were found.