After the Ice Age, the Baltic Sea washed the rocks of Teijo. These bare hills add diversity to the landscape and the natural features of the National Park. On the rocks of Nenustannokka, Inskeri and Lake Matildanjärvi, you find a great scenery. There are rugged pine forests along the hillsides, and pine bogs growing the Marsh tea (Ledum palustre) and the Bog Bilberry (Vaccinium uliginosum) in depressions. On the lower slopes, there are spruce forests and wet hollows with spruce bogs, and large mires on the lake shores.
Most of the forests in Teijo National Park are young managed pine forests. Even though the area is not very lush in most places, small patches of luxuriant herb-rich forests and gushing springs here and there make the landscape more varied.
In Teijo you can also learn about the ancient phases of the Baltic Sea, as the ancient seashore can be still seen in Jeturkasti and Miilunummi.
In the National Park, there is one eutrophic fen, which is a type of mire that has almost disappeared in southern Finland. The most fastidious plant species of the fen include the Broad-leaved Cotton-grass (Eriophorum latifolium), the Dioecious Sedge (Carex dioica), the Common Yellow Sedge (Carex demissa), the Cotton Deergrass (Trichophorum alpinum) and the Marsh Arrowgrass (Triglochin palustris). On the spring fen grows the threatened Bog Pondweed (Potamogeton polygonifolius). In several places in the National Park you can also find the Alpine Campion (Lychnis alpina) and the Hazel (Corylus avellana).
The most common fish species in the lakes of Teijo are the Perch (Perca fluviatilis) and the Pike (Esox lucius). There is a Freshwater Crayfish (Astacus astacus) population living in the lakes of the National Park, and more of them have been planted by Metsähallitus. The planted Crayfish have made the existing population stronger, and special crab catching trips are now organised for groups on Lake Matildanjärvi.
Nesting birds of the area include the Canada Goose (Branta canadensis), the Crane (Grus grus), the Wood Sandpiper (Tringa glareola) and the Black Grouse (Tetrao tetrix). Mammal species living in Teijo include the Moose (Alces alces), the White-tailed Deer (Odocoileus virginianus), the Roe Deer (Capreolus capreolus) and the Lynx (Lynx lynx).