Fort Chepe was established in 1603 by Governor Alonso de Ribera on the hill west of Concepción, overlooking the mouth of the Biobío river. For two centuries it was the key Spanish stronghold on the frontier with Mapuche territory, repeatedly garrisoned, attacked and rebuilt.
Little of the original fort survives — what you find on Cerro Chepe today is a mix of earthworks, archaeological remnants and a small interpretation panel — but the hill itself offers good views across the river and back to the city. It's a short detour for anyone interested in the Arauco War or the long Spanish-Mapuche frontier that defined this part of Chile.