La Muralla Roja — the Red Wall — is a postmodern apartment complex designed by the Catalan architect Ricardo Bofill and completed in 1973. Painted in vivid shades of pink, red, and blue that stand out against the sky and sea, the building has become one of the most photographed pieces of architecture on the Costa Blanca, attracting architecture students and Instagram photographers in roughly equal numbers.
The complex is private residential property, so you cannot wander freely inside, but the exterior and the stairways that face the sea are accessible from the road. It sits at the base of the Penon de Ifac on the south side of town, near the Playa de la Fosa. Worth seeking out if you have any interest in architecture.