The castle hills situated north of Old Porvoo are significant ancient monuments. Iso Linnamäki (Great Castle Hill) is the site of one of the biggest ancient fortresses in Finland, while on Pikku Linnamäki (Lesser Castle Hill) there is an Iron Age burial site, discovered in 1965. Iso Linnamäki is criss-crossed by many paths and there are also now dried up moats, which can still be seen, with wooden bridges across them. There you can also spot the great pine with its twisted roots that artist Albert Edelfelt depicted in his painting ‘Porvoo seen from Linnamäki’.

At the foot of the Linnamäki hills is Maari Park, a favourite among Porvoo residents for walks and picnics.