Caldara di Manziana, Volcanic nature reserve near Manziana, Italy.

Caldara di Manziana is a protected nature reserve near Rome with active volcanic vents that release carbon dioxide, hydrogen sulfide, and methane from below the surface. The site features marked walking paths through forest areas, allowing visitors to observe the geological features and the surrounding woodland environment.

The site formed around 600,000 years ago as part of the Sabatini volcanic system, which shaped central Lazio and created Lake Bracciano. This ancient volcanic activity left the geological structures visible today that visitors can explore.

The name Manziana derives from Manth, the Etruscan god of the underworld, to whom the territory of Manziana and Canale Monterano was consecrated; the Silva Mantiana forest took its name from him, and the nearby Bosco Macchia Grande is its only surviving sector. The dark, impenetrable forest and the sulfurous springs, once seen as an emanation of the subterranean world, likely explain the link with the god.

Access is via marked trails through the Manziana forest, with the full walking circuit taking about two and a half hours. Wear sturdy footwear and watch for wet areas near the gas vents.

The protected area contains an unusual grove of white birch trees growing around swampy terrain, a rare combination in the Mediterranean climate. These trees thrive due to the moist conditions created by volcanic activity and soil composition.