Situated 9 km away from the center of Oñati is the Arantzazu Sanctuary. The sanctuary was built over 500 years ago in honor of the Virgin Mary that supposedly appeared there to a local shepherd in the 14th century. A new impressive basilica was built in the 1950s on the edge of the cliff and is one of the best example of Basque avant-garde architecture: entrance gates by Eduardo Chillida, sculptures of apostles by Jorge Oteiza, altarpiece by Lucio Muñoz.
If you are into hiking, the Arantzazu Sanctuary is the perfect starting point. Located within the Aizkorri-Aratz Natural Park, there are lots of trails of different levels that will allow you to discover spectacular landscapes of unique beauty. For example, you can hike to the top of the Aizkorri peak in about 3 hours.
Ask in the tourism office for a publication called “Senderos de Oñati” with more information about existing trails.