The Compañía Cervecera de Puerto Rico — universally known as the India brewery — has been brewing beer in Mayagüez since 1937 and is the largest brewery on the island. The factory is a working industrial site, not a tourist trap, but you can usually tour it on weekdays by booking ahead at the reception. The tour covers brewing, packaging, and a tasting at the end.
Even without the tour, the brewery building is part of the city's twentieth-century identity. The huge red India sign on the chimney is one of the landmarks you see flying into Mayagüez airport.