Kostivere limestone karst area, where the Jõelähtme River flows under the ground, is one of the largest in Estonia – 2.9 km in length and 0.5 km in width and very rich in different interesting karst formations.
It is possible to find a lot of little karst caves here. The most frequent formations that can be found here are niches and hollowed-out parts of the riverbank, which represent transitional karst formations between the surface and underground. The most extensive of these are located in the middle part of the karst area. Karst caves also include hollows under natural bridges. There are four caves in Kostivere karst area. The largest of them is Karjakelder, which is 6 m in length, up to 4 m in width and 2.5 m in height.