Baths of Caracalla
The Baths of Caracalla were Roman public baths, or thermae, built in Rome between 212 and 216 CE, during the reign of the Emperor Caracalla. The extensive ruins of the baths have become a popular tourist attraction.
The complex was 225 m (740 f) long, 185 m (390 f) wide and 385 m (125 f) estimated height, and could fit anywhere from 2000 to 3000 bathers. It consisted of a frigidarium (cold room), tepidarium (medium), and caldarium (hot room), as well as two palaestras (gyms where wrestling and boxing was practiced). Also part of the complex is an aqueduct (for the thermae or water reservoirs), where water was brought in.
The Caracalla bath complex of buildings was more a leisure centre than just a series of baths. The "baths" were the second to have a public library within the complex. Like other public libraries in Rome, there were two separate and equal sized rooms or buildings; one for Greek language texts and one for Latin language texts.
The building was heated by a hypocaust, a system of burning coal underneath the ground to heat water provided by a dedicated aqueduct. It was in use up to the 19th century.
In the early 20th century, the design of the baths was used as the inspiration for the design of Pennsylvania Station in New York City by the architect Charles McKim. As well as Louis Kahn's Jatiyo Sangshad Bhaban (National Assembly Building) in Dhaka, Bangladesh.
The ruins stand as the backdrop for the Teatro dell'Opera di Roma in the summer opera season.
It has also become a venue for modern cultural events, such as the gymnastics competition during the 1960 Summer Olympics in Rome. And the concert of the Three Tenors at the conclusion of the 1990 World Cup.
 
From: www.wikipedia.org