Since at least the 18th century, grotesque has come to be used as a general adjective for the strange, mysterious, magnificent, fantastic, hideous, ugly, incongruous, unpleasant, or disgusting, and thus is often used to describe weird shapes and distorted forms such as Halloween masks. In art, performance, and literature, however, grotesque may also refer to something that simultaneously invokes an audience feeling of uncomfortable bizarreness as well as sympathetic pity.
Grotesque studies, Michelangelo
Roman frescos in Nero's Domus Aurea, Rome, unknown painter, c. 64–68 AD
Ceiling of the Piccolomini Library, Siena Cathedral, Siena, Italy, by Pinturicchio and his assistants, 1502–1503
Pilgrim bottle, by the Fontana workshop from Urbino, Italy, c. 1560–1570, tin glazed earthenware (majolica), Victoria and Albert Museum, London
A grotto 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 often flooded at high tide. Sometimes, artificial grottoes are used as garden features. The Grotta Azzurra at Capri and the grotto at Tiberius' Villa Jovis in the Bay of Naples are examples of popular natural seashore grottoes.
Eternal Flame Falls in New York has an eternal flame inside a small grotto behind the falls
Grutas de García in Nuevo León, Mexico
Two vaulted grottoes called Taq-e Bostan, located in Iran, Sassanian era
Grotto in Cevio