San Julián and Santa Basilisa Parish Church in Isla, Arnuero. One of Cantabria's finest hall-shaped column churches.

The 16th-century church was restored in 1629 and 1685–1690. The archbishop of Burgos, Juan Fernández de Isla, encouraged the latter work, and Francisco del Pontón Setién, the master builder, collaborated with Bernabé de Hazas on the design.

The temple was named a Monument Asset of Cultural Importance on 4 April 2002, and the BOC published the proclamation on 18 April.

Renovated in 2010.

The middle nave is wider than its three equal-height naves with four bays. The polygonal chevet and quadrangular tower at its base break up the naves' exterior volume.

The interior supports are circular pillars with plinth, attic base, and Tuscan capital, with recessed pilasters like those in the parish church of Ajo.

The center nave, transept, and side naves use semicircular and pointed arches, respectively. These quadrangular arches have recessed soffits. Most nave sections have simple star-shaped ribbed vaults.

Its key components are worth emphasizing.

In the church's base, the tower resembles Transmeran towers. Three levels with overhanging cornices create its amazing height. Classicist pilasters frame the upper floor's ashlar walls and apertures. The last section has a Herrerian ball-topped balustrade. Eventually, a stone pyramid surrounds the tower.

On the second section of the epistle aisle, a magnificent semi-circular arch with a triangular pediment frames the doorway. Baroque elements complement classicist ideas.

One of Cantabria's best examples of classicist architecture, this church has a 17th-century saloon floor plan.

The church's altarpiece. An outstanding 17th-century polychrome altarpiece. It's large and decorative. Its composition adapts to the polygonal shape of the apse and features a triple crown or attic that follows the line of the three streets—two lateral, a central, and two inter-aisles—organized in a little predella and two parts. Free-standing sculpture alternates with reliefs. The Virgin's life reliefs and the predella's Last Supper, Prayer in the Garden, and Entrance into Jerusalem stand out.