There are many archeological remnants in Oskarshamn. Just the other day I went to see the rock carvings/petroglyphs somewhat to the east of the city. They are from the younger bronze age, around 900-500 BC and depicts ships and footsteps.
As they are placed on a strip of land between two bogs and as the custom of the era was to perform sacrifices on such places one might think that they are part of some old ritual of the long gone past.
Direction: Drive the Road 23 westwards, passed the hospital. After about 7 km there is a road to the left, marked "Fliseryd" and a sign for a golf course. Turn left there and follow the road for 500-600 metres. On the left of the road there is a small path and a tiny blue sign saying "Hällristning". Turn onto the path, park the car and walk the 600 metres left before the carvings. There are signs near the carvings in swedish, english and german.