Lake Avernus, Volcanic crater lake in Campania, Italy.
Lake Avernus is a volcanic crater that forms part of the Phlegraean Fields near Naples. The water sits about 130 feet (40 meters) below the surrounding terrain, with steep rocky walls and forested slopes meeting the shore.
The lake formed from volcanic activity in ancient times and was dramatically altered by Roman engineering. In 37 BC, the Romans built a canal to connect the basin to the sea, creating a major naval port that served their fleet.
The lake held deep meaning for ancient peoples who saw it as a gateway to the underworld. Toxic volcanic gases rising from the crater killed birds flying overhead, which reinforced the frightening reputation of the place.
Visitors can reach the lake on foot or by car, though it is helpful to allow extra time for breaks since paths and stairs can be strenuous. Coming early in the day during hot months is wise, and bringing plenty of water is essential.
A tunnel carved through stone near the lake in Roman times remains one of the longest such passages ever created by hand in that era. This underground passage connected two harbors and demonstrates Roman engineering skill in working through difficult terrain.
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