This sprawling detention center is located in the province of Álava in the north of Spain. The original facility was built in 1940 and by 2007 held more than 50% of detainees in the Basque Country. Problems with overcrowding led to the decision to build a new prison with a much greater capacity. The project was managed by Exeteco on behalf of BSWi. Construction started in 2008 and the facility was finally inaugurated in 2011.

The revolutionary center was built on a plot of 440,000 m² plot of land with an 85,000 m² built area. It has 720 residential cells each measuring 13 m², and 152 additional cells that serve as arrival, isolation, and infirmary units. Each residential cell can accommodate two inmates (1,440 in total), while the auxiliary cells can each house an additional detainee (152 in total).

Nanclares de Oca is a maximum-security prison that employs cutting-edge security systems, including a three-kilometer perimeter with five sets of fences, six-meter-high walls and over 200 CCTV cameras. It was built using modular units to facilitate the separation of inmates based on the severity of their crimes and their assigned risk level.

Each unit is completely independent from the others and boasts all the services and facilities required to support treatment and rehabilitation programs. The prison has a kitchen and laundromat, a sociocultural area and a hospital with treatment rooms, wards and a pharmacy.

The facility also boasts a number of recreational facilities including a sports center with a gym and a swimming pool, a library and classrooms for IT and music lessons. To further encourage rehabilitation and reduce recidivism rates, the prison has several production plants used by inmates to manufacture products for both internal and external use.