grotto

A grotto (Italian grotta and French grotte) is a natural or artificial cave used by humans in both modern times and antiquity, and historically or prehistorically. Naturally occurring grottoes are often small caves near water that are usually flooded or liable to flood at high tide. Sometimes, artificial grottoes are used as garden features. The Grotta Azzurra at Capri and the grotto at the villa of Tiberius in the Bay of Naples are examples of popular natural seashore grottoes.
Whether in tidal water or high up in hills, grottoes are generally made up of limestone geology, where the acidity of standing water has dissolved the carbonates in the rock matrix as it passes through what were originally small fissures. See karst topography, cavern.

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