The burial site of Käku with its stone circle graves is located near the namesake Käku village in the parish of Kaarma in the middle of Saaremaa, 2.5 km NW from the Kaarma hill-fort and nearby church. The approximate dimensions of the burial site are 180 m (S-N) x 60-100 m (S-W). The whole area is densely covered with around 10-20 cm high round stone barrows, with a diameter of 5-7 m. A great part of the site has been destroyed or forested by now.
The stone circle graves of Käku were first excavated in the 1920s (by Aarne Michael Tallgren and Harri Moora), but bigger-scale archaeological excavations took place there in 1948-1949 (by Leo Metsar). Metsar discovered nine stone circle graves and several burial patches in the area between them. The stone layers of the graves were quite thin and were made mostly of one or two layers of limestones or granite boulders. When walls of limestone slabs consisted of 2-3 layers, the slabs were sometimes collapsed outwards. The stone circle graves at Käku were not filled with head-sized granite stones, as was otherwise characteristic of most other stone graves in Saaremaa. Instead, they were filled with soil mixed with pebbles and shingles. The distance between graves was 2 to 4 m.
The bone material and artifact pieces from the Käku burial site were heavily burned and fragmental. Most of the finds could be dated to the 11th century, some to the end of the 10th or to the beginning of the 12th century. Unlike Late Iron Age stone graves without formal structures, which also were widespread in Saaremaa, the Käku graves presumably included individual burials, although there are no scientific analyses to prove it.
The humans buried in the Käku graves lived probably 800-900 meters away in the same area of the modern-day Käku village. There has been recorded a cultural layer in the village dating to the 10th-12th century and later. Additionally, remains of a smithy have been excavated near the village, which has been dated to the 14th-17th century.