Castle ruins at Hammersta
The fourteenth-century ruins of Hammerstahus lie south of Hammersta farm. The castle was probably built by knight Eringisle Nilsson the Elder in the fourteenth century. The entrance was high above the ground and could only be reached by a removable wooden staircase. The castle was abandoned during the 15th century: only the lower floor with its 1-metre-thick walls remains. The reserve has also four burial grounds and three prehistoric settlements.
A cave known as “Frugrottan” or “Frubergsgrottan” can be found in the western slope of Fruberget. It is necessary to climb to reach the cave, which is 10 metres long and 5 metres high, and the entrances can be difficult to find. It is a good idea to bring a torch. Tradition says that Frugrottan is named after a mistress of Hammersta who took her riches and livestock into the cave in order to escape from persecutors.