San Nikolas Eliza, also known as the Church of San Nicolás, is a prominent Baroque-style church located in Bilbao's Casco Viejo (Old Town). Completed in 1756 after thirteen years of construction under the direction of master builder Ignacio de Ibero, the church is renowned for its unique architectural design and historical significance.

The church's floor plan is distinctive, featuring a Greek cross shape inscribed within a square, an uncommon design for its time. This layout is crowned by a magnificent dome with a chamfered prism shape, though its visibility from the front is partially obscured by the central belfry on the main façade. The façade itself is divided into three sections: the central entrance and two flanking towers. Notably, the tympanum above the main entrance showcases a bronze relief, adding to the façade's elegance.

Inside, visitors can admire five exquisite Rococo-style altarpieces crafted by Juan Pascual de Mena. The central altarpiece in the high chapel features a figure of Saint Nicholas of Bari, accompanied by representations of Saint Laurence, Saint Vincent, the crucified Christ, Saint Peter, and Saint Paul. Flanking the central pinnacle are impressive sculptures symbolizing Charity and Fortitude. These altarpieces were meticulously restored between 2007 and 2011, ensuring their preservation for future generations.

Historical Significance Beyond its architectural beauty, San Nikolas Eliza holds a special place in Bilbao's history. In 1812, it served as the venue where the General Assembly of Biscay signed the Cádiz Liberal Constitution, popularly known as "La Pepa." Additionally, during the Carlist Wars, the church was repurposed as a munitions store, forge, and workshop, yet it emerged largely unscathed, allowing visitors today to appreciate its original design and elegance.

The church is open daily, typically from 10:00 to 13:00 and from 17:00 to 19:00, though these hours may vary on holidays or during religious events. Entrance is free.