The Bolunburu area of Zalla is located on a bend on the left bank of the river Cadagua.
The track that takes us there is located in part on the old Bilbao-Balmaseda royal road, whose cobblestones are visible close to the church. The site is made up of a
foundry, a mill and the
small church of Santa Ana. This church was built in the post-mediaeval period in 1612. Its layout is rectangular, with a gable roof and it was built using stonework and masonry. Its archaeological value lies in the burial sites around it.
The tower-house at Bolunburu, from the Late Middle Ages, has interior beam work in a good state of repair.