The Arenas Bridge is a truss bridge built in 1894 between the municipalities of Cayey and Cidra in Puerto Rico. Also known as Puente Rio La Plata, it was the longest bridge constructed in Puerto Rico during the Spanish colonial period. It crosses the Rio de la Plata, the longest river in Puerto Rico. According to the U.S. National Park Service, "[t]his is the most important metal bridge in Puerto Rico from the period." The bridge is still standing.

Cayey, officially Cayey de Muesas, is a mountain town and municipality in central Puerto Rico located on the Sierra de Cayey within the Central Mountain range, north of Salinas and Guayama; south of Cidra and Caguas; east of Aibonito and Salinas; and west of San Lorenzo. Cayey is spread over 21 barrios plus Cayey Pueblo. It is part of the San Juan-Caguas-Guaynabo Metropolitan Statistical Area.