Kastelli at Linnankangas, Pattijoki, is situated on an imposing moraine ridge in a forest landscape typical of northern Ostrobothnia, with pine forests alternating with open marshes. This type of construction, which according to legend was built by giants, is only found in the coastal areas of the gulf of Bothnia. There are about 30 known constructions of this kind. Kastelli at Pattijoki is the largest of them; it is a rectangular rampart measuring 36 x 62 meters built in an area which used to be a rocky shore. The rampart, which is two meters high in its present state, has six gateways.
In the environs are more than twenty rock cairns, a representative group of ten trapping holes and a stone age dwelling site lower on the slope. Excavations were made at Kastelli in the 1920s. The findings, especially the schist material, date the "giant's church" of Kastelli at about 2000 BC.
Kastelli at Pattijoki represents the earliest monumental construction in Finland in a form which is rarely found in hunter-catherer cultures. It is likely that the construction was related to the hunting of seals on spring ice away from dwelling places. The rampart is surrounded by stone cairns, which probably represent the remains of holes made for the keeping of killed animals. Having demanded a great deal of work to construct, Kastelli is a concrete manifestation of social organisation in Finland during the Stone Age. Althought it is now situated close to present habitation, this enormous ancient monument complexe has been preserved nearly in its original and natural state.