A nymphaeum or nymphaion, in ancient Greece and Rome, was a monument consecrated to the nymphs, especially those of springs.
The Jerash nymphaeum
The Nymphenbad of the Zwinger palace in Dresden, Germany
Nymphaeum of the Villa Giulia in Rome
The nymphaeum at Villa Barbaro in Maser, Veneto, Italy
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