The Tönnönkoski rapids of Orimattila are in the village of Tönnö in a nationally listed cultural landscape. The long history of settlement in the Porvoonjoki River valley is evident here. Archaeological surveys have revealed numerous Stone Age dwelling sites in the vicinity of the rapids.

The earliest information on a mill built in the rapids is from 1586. As many a four mills have operated at the same time in the rapids. At present, there are two flour mills and the remains of a sawmill. The older mill (Niemen mylly) is from the 19th century. It went out of use in 1967. The later mill, known as Tönnön mylly, dates from the early 1900s and is still in use. The river is crossed by Finland's oldest reinforced-concrete arch bridge from 1911. 
Next to the bridge is an information sign on the history of the region. 
Tönnön luontopolku - The Tönnö Nature Path (in Finnish)

The Myllykoski rapids at Virenoja

The Myllykoski rapids are located in the village of Virenoja in Orimattila. A Stone Age dwelling site has been discovered near the rapids. The later use of the area is represented by the ruins of a mill and the miller's cabin. According to documentary sources, there was a mill in year-round use at Virenoja already in the late 16th century.

A sawmill was established at Virenoja in 1904. It was fitted with an electric generator in 1919, but owing to overload it was destroyed before long in the 1920s. The mill was discontinued in the late 1970s, and now only its foundation remains. The ruins and the surviving miller's cabin nearby are privately owned.

There is an information sign on the history of the area next to the ruins of the mill.