Forte Marechal Hermes, Coastal fortress in Macaé, Brazil.

Forte Marechal Hermes is an open-air octagonal battery on the 50-metre-high morro da Fortaleza, south of the Macaé River mouth between Imbetiba and Conchas beaches, facing the Sant'Anna archipelago. Its open command post links acoustically by galleries to the casemated service magazines of four Armstrong 154.4 mm guns on the upper level. The Pavilhão de Comando dates from 1939, and the Portão das Armas, reinaugurated in 1958, is flanked by two 152.4 mm guns deactivated in 1997.

Construction of the fortress began in the late 1800s with an octagonal battery design to defend the river entrance. It received its current name in 1911 to honor a Brazilian president and was later expanded with additional structures.

The fortress complex reflects how its spaces were organized for daily military operations, with different structures serving specific functions across the site. Walking through reveals how soldiers once moved between the various buildings and positions.

Visitors should expect slippery surfaces, especially after rain, and wear solid footwear to safely navigate the grounds. Shade is limited on the site, so bringing sun protection and plenty of water is advisable.

The open-air command post on the upper level communicated with the four casemated magazines of the Armstrong 154.4 mm guns through acoustic galleries, not tunnels. Visitors can still see these galleries cut into the battery, a detail often mistaken for an underground passage network.