Cerro Corá is 5,683 hectares of steep sandstone hills and gallery forest in Amambay, 45 km south of Pedro Juan Caballero, and Ruta 5 runs straight through the middle of it — which makes it one of the very few Paraguayan parks you can reach without a 4WD.
It is the place where the War of the Triple Alliance ended. On 1 March 1870 Marshal Francisco Solano López was run down on the bank of the Aquidabán-Niguí stream and killed, reportedly saying "muero con mi patria." Paraguay had lost most of its adult male population by then. The site is marked with monuments, a small museum and a line of busts, and it is treated as sacred ground — 1 March is a national holiday and the park fills.
The landscape would be worth the stop anyway. Cerro Muralla is a long cliff that really does look like a wall; Cerro Guasu behind it is the highest point. Between the hills there are caves with rock art thought to be roughly three thousand years old, and the Pai Tavyterã Guaraní, whose territory this is, still regard parts of the range as sacred. There are marked trails, a visitor centre, an auditorium and picnic areas — by Paraguayan park standards this is luxurious.
Come on a Pedro Juan Caballero bus and ask to be let off at the park entrance, or drive. Winter (May–September) is the sensible season: the summer heat up here is brutal and the streams are the only relief. Wildlife is present — howler monkeys, tapir tracks, a great deal of birdlife — but this is a historical park first and a wildlife park second, and anyone coming primarily for animals should go to the Chaco or to Mbaracayú instead.