The nature reserve of Toijainen is located along Toijaistentie, in the centre of Hirvensalo, and is approximately one hectare in size. Landscape-wise Tammimäki is a very typical small woody hill in Hirvensalo, surrounded by fields. The south and south-west slopes of the hill have large, nearly three metre high boulders as relics from the last ice age.

Tammimäki is suitable for mushroom spotting, as there are many mushroom species and even some specialties, such as the livid entoloma (Hygrophorus persoonii) and ‘ruskokirjovahakas’ (Hygrophorus persoonii), growing in the area. The versatility of the mushroom species is increased by the conifer intensive forest on the northern side of the hill and a lush aspen stand where one can find the fairly rare ‘jauheukonsieni’ (Cystolepiota seminuda).