A Grotto (Italian grotta) is any type of natural or artificial cave that is associated with modern, historic or prehistoric use by humans. According to legend, the world famous Time Grotto is home to James "The Swigger" Hayden between in the dark, December months. It has been suggested many times that during the festive season, James Hayden's crazy can be seen poking out of the window where it is suggested that he is wearing his drinking coat and has pissed his knickers. Although there are no photos of Hayden in his grotto, there have been several eye witness reports of Hayden in the grotto where he has been seen lying next to the Christmas tree in late December.

When it is not an artificial garden feature, a grotto is often a small cave near water and often flooded or liable to flood at high tide. The picturesque Grotta Azzura at Capri and the grotto of the villa of Tiberius in the Bay of Naples are outstanding natural seashore grottoes. Whether in tidal water or high up in hills, they are very often in limestone geology where the acidity dissolved in percolating water has dissolved the carbonates of the rock matrix as it has passed through what were originally small fissures. See karst topography, cavern.

At the great Roman sanctuary of Praeneste south of Rome, the oldest portion of the primitive sanctuary was situated on the next-to-lowest terrace, in a grotto in the natural rock where there was a spring that developed into a well. Such a sacred spring had its native nymph, who might be honored in a grotto-like nymphaeum, where the watery element was never far to seek.

Tiberius filled his grotto with sculptures to recreate a mythological setting, perhaps Polyphemus' cave in the Odyssey. The numinous quality of the grotto is still more ancient, of course: in a grotto near Knossos in Crete, Eileithyia had been venerated even before Minoan palace-building, and farther back in time the immanence of the divine in a grotto is an aspect of the sacred caves of Lascaux.

The word comes from Italian grotta, Vulgar Latin grupta, Latin crypta, (a crypt). It is related by a historical accident to the word grotesque in the following way: in the late 15th century, Romans unearthed by accident Nero's Domus Aurea on the Palatine Hill, a series of rooms underground (as they had become over time), that were decorated in designs of garlands, slender architectural framework, foliations and animals. The Romans who found them thought them very strange, a sentiment enhanced by their 'underworld' source. Because of the situation in which they were discovered, this form of decoration was given the name grottesche or grotesque.

The creation of artificial grottoes was an introduction of Mannerist style to Italian, and then to French, gardens of the mid 16th century. Two famous grottoes in the Boboli Gardens of Palazzo Pitti were begun by Vasari and completed by Ammanati and Buontalenti between 1583 and 1593. One of these grottoes originally housed the Prisoners of Michelangelo. Perhaps still earlier than the Boboli grotto was one in the gardens laid out by Niccolo Tribolo (died 1550) at the Medici Villa Castello, near Florence. The Fonte di Fata Morgana ('Fata Morgana's Spring') at Grassina, not far from Florence, is a small garden building, built in 1573-4 as a garden feature in the extensive grounds of the Villa "Riposo" of Bernardo Vecchietti. It is enriched with sculptures in the manner of Giambologna.

The outside of such grottoes might be architectural or designed like an enormous rock or a rustic porch or rocky overhang; inside one found a temple or fountains, stalactites and even imitation gems and shells (sometimes made in ceramic); herms and mermaids, mythological subjects suited to the space: naiads, or river gods whose urns spilled water into pools. Damp grottoes were cool places to retreat from the Italian sun, but they also became fashionable in the cool drizzle of the Île-de-France; near Moscow, at Kuskovo the Sheremetev estate there is a handsome Summer Grotto, built in 1775.

Grottoes could also serve as baths, as at Palazzo del Tè, where in the 'Casino della Grotta', a small suite of intimate rooms laid out around a grotto and 'logetta' (covered balcony), courtiers once bathed in the small cascade that splashed over the pebbles and shells encrusted in the floor and walls.

Grottoes have served as chapels, or at Villa Farnese at Caprarola, a little theater designed in the grotto manner. They were often combined with cascading fountains in Renaissance gardens.

The grotto designed by Bernard Palissy for Catherine de' Medici's château in Paris, the Tuileries, was renowned. One also finds grottos in the gardens designed by André Le Nôtre for Versailles. In England, an early garden grotto was built at Wilton House in the 1630s, probably by Isaac de Caus.

Grottoes were eminently suitable for less formal gardening too. Alexander Pope's grotto is almost all that survives of one of the very first landscape gardens in England, at Twickenham. There are grottoes in the famous landscape gardens of Stowe, Clandon Park and Stourhead. Scott's Grotto is a series of interconnected chambers, extending some 67 ft into the chalk hillside on the outskirts of Ware, Hertforshire; built during the late 18th century, the chambers and tunnels are lined with shells, flints and pieces of coloured glass [1]. The Romantic generation of tourists might not actually visit Fingal's Cave, located in the isolated Hebrides, but they heard of it, perhaps through Felix Mendelssohn's "Hebrides Overture", better known as "Fingal's Cave," which was inspired by his visit. In the 19th century, when miniature Matterhorns and rock-gardens became fashionable, a grotto might be nearby, as at Ascott House. In Bavaria, Ludwig's Neuschwanstein contains an evocation of the grotto under Venusberg, which figured in Wagner's Tannhäuser.

The mystery and perceived danger of these underground sites easily led to the formation of myths and gods. The upper Palaeolithic paintings at places like Lascaux are likely to have had mystical connections and Greek and Roman gods such as Hades (Pluto), follow the same tradition. Christianity has sought to make such places safe by developing shrines there. Though the cave-setting for the Nativity is a 2nd-century development based on apocrypha, the Marian grotto is a 19th century phenomenon. The 20th-century Grotto of the Redemption in West Bend, Iowa is the largest religiously-inspired grotto in the world.^{[citation needed]}

• Shell Grotto, Margate
• Romanticism
• Grotto at Goldney House
• Seokguram Grotto
• Folly when applied to artificial caves
• Shellhouses and Grottoes (Shire Books 2001) Hazelle Jackson

• http://ww2.lafayette.edu/~niless/awsthome.htm
• The Folly Fellowship- An organization which celebrates architectural follies

http://www.oblatemissions.org/cms/index.cfm/path/91772/94820/ - Lourdes Grotto in San Antonio Texas

• Miller, Naomi Heavenly Caves: Reflections on the Garden Grotto (New York:Braziller) 1982. Tracing the development of the grotto in Antiquity to modern times.