Mantere Hillfort is an ancient castle in Hämeenlinna. It rises more than 50 meters above the lake shore of Lake Katumajärvi. The Hillfort slope is very steep on the lake side, but the west side is more gently sloping. At the top of the hill are walls made of rocks, which are remnants of an ancient fortification. In the middle of the rocky walls, there are also two ports. It is estimated that the ancient castle was in use during the Iron Age and time of vikings in the 800-1000's. There are wonderful views over Lake Katumajärvi from the top of the Mantere Hillfort. The hillfort can be reached via the forest trails starting from the Hämeenlinna-Turenki road (regional road 290).