Aittosaari is located in the northern part of the municipality of Viitasaari, on the eastern shore of the lake Keitele. The total area of Aittosaari island is approximately seven hectares. The Foundation previously owned just over four hectares on the island, which it purchased from UPM in April 2010. The latest purchase in 2020 allows the Foundation to protect an additional area of approximately three hectares, meaning that the entire island is now protected.
The nature on Aittosaari island is varied: grassy heaths with lush spruces and broadleaf trees, rugged pine woods, lichen-covered rocks with old pine trees, and a strip of beautiful beach. The forest has not been cleared around the buildings, so they are beautifully surrounded by the trees, and also well camouflaged from the lake. In addition to protecting biodiversity, protecting Aittosaari is also important for the landscape. Other islands located near Aittosaari, such as Honkasaari, have also been protected.