The old bridge of Alvettula in the eponymous village in Hauho, halfway between the cities of Tampere and Lahti. One of the first reinforced concrete bridges in Finland, built in 1916; only two even older ones remain.
The bridge is built according to a rather unusual design of engineer Tapani, from hollow blocks, into which rebars were pushed and then everything was filled with concrete. Well, to be fair, I don't really know exactly how unusual that is. There was not enough engineering skill available at the time in Finland, and the bridge was built rather haphazardly; already in 1931 it demanded major repairs.
A battle took place here in the Civil War of 1918; the Reds, already crushed in the decisive battle of Tampere, managed to break through the Whites-held bridge towards Lahti and Russian border, taking more heavy losses. A new bridge on this road was built in 1970. The old one was planned to be demolished, but the locals successfully lobbied for preservation, and now it stands parallel to the newer one and has museum status. One of the old crossroads signs from the 1930s, of the kind I really like, also still stands by the bridge: