Not far from Valdivia, and worth a visit, are the Spanish forts at Niebla and Corral. The river that divides these two forts still has a sunken ship further in that was swept up by the massive earthquake that hit Valdivia in 1960. The earthquake caused massive damage to the area.
To view the forts you can get to Niebla by car or bus. To get to Corral you should take a ferry across.
The Castillo de Niebla is a 30 minute drive approx outside of Valdivia towards the coast. It is the ruins of an old fort which is now a preserved monument and tourist attraction. There are the remains of some of the barracks which now houses a museum with maps, paintings and ornaments and outside there are old gun establishments.
There is a small admission fee.