Apart from this ensemble, Castro has high quality examples of 19th and 20th century architecture. On the low part of the church is Los Chelines, a Modernist and Gothic Revival work by Severino Achúcarro. Opposite, the 18th century Town hall is located. It is a dressed masonry casona with arcade to which Eladio Laredo, an architect from Castro, attached in 1902 the historicist tower which adorns the building. The highly interesting residential ensemble is located behind the sea-front, formed by an eclecticist palace, a castle of Gothic Revival, Mudejar inspiration, and an Oriental pavilion (Casonas and montañeses palaces). On the sea-front avenue, one finds the house built for Isidra del Cerro, a "French modern" work by Achúcarro, i.e., of an eclecticism with classic motifs (frontispieces, bull's eyes, dressed stone, etc..) and its typical four-cornered towers, spires, pinnacles, etc.. The house of the former Royal Hotel, built by Eladio Laredo in 1902, is also found. Finally, another interesting building is the regionalist Sotileza chalet.

From Castro Urdiales, driving along the Santander-Bilbao highway to Santander, after a few kilometres, one can take the turning to Guriezo valley which has great artistic richness. The village of Guriezo, is the church of San Vicente de Rioseco, one of the best examples of religious architecture in Cantabria. Further religious buildings in the district are the 16th century church of San Bartolomé in Landeral and the hermitages of San Blas in Revilla and Santa Catalina in Trebuesto. Many 17th to 19th century casonas are scattered throughout the district (the palace-casona of Marroquín, Pinta House, etc.).

Finally, it is worth mentioning the popular architecture of the eastern area with the influence of the Basque caserío, a building with gabled roof, its ridge perpendicular to the façade, a broad eave over the southern main façade and wooden balconies.