The viaduct over the Almonte river is located in the Alcántara-Garrovillas reservoir section. It stretches 6,265 metres and forms part of the Madrid-Extremadura High Speed Line that runs through the municipalities of Garrovillas de Alconetar and Santiago del Campo in Cáceres.
The project consists of building a new high speed double-track platform. Some of its unique aspects include the fact that it crosses over the river Almonte, 996 m long, with a deck fixed upon a 14 metre-wide and 3.10 metre-thick statically indeterminate box section. This traverses the tail water of the Alcántara reservoir where it is met by the river Almonte.
The viaduct is divided into three distinct parts: two access roads and one central section. The central part has a concrete arch with an octagonal section varying in width and thickness with a span of 384 metres.
Once finished, the Almonte Viaduct will be the third largest concrete arch in the world and hold world record-breaking status in railway arch bridges, beating the two German bridges, Froschgrundsee and Grümpen, which have arches spanning 270 m. In comparison with other concrete arch bridges (regardless of use), it will be the third largest in the world behind the Wanxian bridge in China with a 421 m arch, and the KRK bridge in Croatia with a 390 m arch.