Forte Junqueira is a small hexagonal fort with walls three metres thick, sitting within an active Brazilian military base on the riverbank. Despite its compact size, it has a significant history — it was built in 1772 and served as the primary military installation defending Corumbá during the 19th century, including during the Paraguayan War when it was briefly captured and held by enemy forces.
The real reason to visit is the view: from the fort's parapet you can see across the Paraguay River into Bolivia, and the flat Pantanal floodplain stretches in every direction. Access requires coordination with the military base — visit in the morning on weekdays and the base personnel are generally accommodating to tourists. Ask at the Porto Geral excursion offices for current access procedures.