The bath complex covered approximately 25 hectares (62 acres). The complex is rectangular, measuring 337 × 328 meters. Its construction involved the moving of a substantial amount of earth, as parts of the nearby hills had to be removed or leveled into platforms. Several million bricks were used in the construction. The baths contained at least 252 columns, 16 of which had a height of over 12 meters.

The axis of the baths was laid out in a northeast to southwest fashion to make use of the sun's heat. The baths followed the "great Imperial baths" blueprint for Roman baths. They were more a leisure centre than just a series of baths. Besides being used for bathing, the complex also offered facilities for taking walks, reading/studying, exercise and body care.

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Western Peristyle-palastera
The Palasestrae Occidentale (western exercise court), excavated in 1870 CE, were double and symmetric. The palastera floors had colored marble mosaic tesseras with large use of green porphyry (serpentino) and yellow marble (giallo antico). They had extremly varied and original patterns, with curvilinear motifs and a beautiful valute motif in the center made with green porphyry. During the 1824 CE excavations, in the two apses were found the famous mosaics with the athletes in 1963 CE they were transferred to the Vatican Museums were in the 70s they were remounted to their original order and primitive semicircular form, The floors were boarded by black trim and were divided internally in to rectabgular, square and irregularly shaped panels; the first contained life-size portraits of athletes or judges, the second representations of larger than lifesize busts of athletes and the third representations of the equipment and prizes for the athletes. They are immediately distinguished from the judges by their nudity, and according to their attributes, we can recognize the winners, with palm branch and crown, boxers, javelin throwers and wrestlers. The floors on the upper levels were decorated wit marine procession motifs with Nereids, Tritons, dolphins, cupids and marine monsters. It was about three hundred meters long. It collapsed frome the upper floors and now lies in large fragments leaning against the walls of the two palastera.

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Natatio
The natatio was a large uncovered pool (50 x 22 meters) with cold and shallow water. The walls were higher than 20 meters and were decorated by two overlapping rows of niches filled with statues, speparated by giant columns. Bathers used to play games on the edges of the pool. There are still visible remains of a tabula lusoria (inspect), a game engraved on a marble step.

The natatio, a truly olympic-sized swimming pool, must have been another impressive structure. Its northern facade was divided into three sections by gigantic grey columns. Each section contained six statue niches (three for each of the two levels) divided by orders. The lower order was made with column drums of Carystian marble, the upper one of Granito del Foro. The conduits for the water that ooured in to the swimming pool can still be seen in the line of niches on the ground floor. The pool was on impressive dimensions with walls over 20 meters high on its short sides it was entered by steps and was not very deep and so not suitable diving. The area can be compared stylistically with the frons scenae of the Hellenistic theatres, but also with a mocument closer to it in both topographical and chronological terms, namely the septizodium, built by Caracalla's father, Septimius Severus on the slopes of the Palatine. On one of the steps of natatio is still visible a tabula lusoria, an ancient Roman game both for adults and kids; this was made by a wooden board or often (a here) drawn or incised on the steps of public buildings.

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Central Sphaeristerium and Wresteling Halls

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Frigidarium
The central room was the frigidarium, whose high roof was supported by eight giant columns made from Egyptian granite. Walls and floor were made from marble. The hall served a dual purpose: It was a meeting place and transition area for visitors heading for other parts of the bath. It also housed the cold baths, in the form of four pools, two of which were connected to the tepidarium and two of which communicated with the natatio via some waterfalls. In the middle of the frigidarium was another circular pool (now at the Archaeological Museum at Naples) surrounding a fountain. It was flanked by two additional brick pools.

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Caldarium
The caldarium was a circular room with marble floors and topped by a dome of almost 36 meters diameter, close to the size of the Pantheon's dome. The weight of the dome was carried by just eight masonry pillars. Between them were glass windows that helped heat the large room (and reduced the weight of the walls). Its seven pools measured 9.5 × 5 meters (depth of 1 meters). Only six of these remain. The seventh was replaced by a small apse during the restoration by Constantine.

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Western Library hall
The baths of Caracalla were the second establishment to have a public library within the complex. The surviving library structure measures 38 × 22 meters. This library had three walls covered by niches (a total of 32) that housed the books. A larger niche in the middle of the southern wall likely contained a statue. A masonry ledge in front of the three other walls probably served as a bench. The floor is made from marble.

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.

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Mithraeum
The Mithraeum at the baths is considered the largest documented gathering space for the worshippers of Mithra, the Persian god in vogue with the military and mostly lower-class men, in the 2nd and 3rd centuries CE. The mithraeum was approximately 23 meters (75 feet) long and 10 meters (33 feet) wide with a cross-vaulted ceiling. It can be only roughly dated by the two main events associated with the baths: the mithraeum was created after the complex was completed circa 217 CE and it was probably no longer in use when the aqueduct supplying the complex was cut in the 530s CE.

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Tunnels