This initiative, now in its fifth edition, seeks to emphasize these riverside constructions in Gipuzkoa and the work of millers. The importance of mills in the social, economic, and industrial development of the territory is underscored, as a crucial part of its historical, technological, anthropological, and ethnographic heritage.

As part of the Mills Day celebration, several mills in Goierri will open their doors to visitors. These include the Ibares mill in Arama, Larruntza in Ataun, Igartza in Beasain, Igaralde in the Brinkola neighborhood of Legazpi, and Errotatxo in Mutiloa. These mills will offer guided tours and various activities.

Additionally, the Igartubeiti museum in Ezkio will join the celebration on Saturday, with an activity focused on elements used to protect farmhouses. The following weekend, there will be a guided visit to the Larraondo hydraulic sawmill in Zerain, a site that once functioned as a mill.