Gymnasion

The most extensive employment of columns in civic architecture was in the porticos, the stoas, which surrounded the market-places and extended through many streets, being connected with baths, gymnasions, palaestras, stadia, and hippodromes, and even appearing as independent buildings.

Source: wiktionary

Spandex had not yet been invented, so swimming, as many other sports, was done in the nude (see earlier discussion about gymnasions).

Source: wiktionary

The gymnasions did not remain training camps, but became places where people could spend time and hold meetings as needed, and it was there that the early Sophists began teaching youngsters. After the Athenian gymnasions, Academy, Lyceion, and Kynosarges became schools of famous philosophers, gymnasions were no longer merely places where naked men conducted physical training and then washed and relaxed, but were also centers for cultural education — if not schools (see below).

Source: wiktionary

The new bathing standard of (some) Late Hellenistic gymnasia is probably reflected in Vitruvius’ description of an ideal Greek gymnasion, which included in the corners of its northern suite of rooms two areas that were physically clearly separated: on one side a traditional loutron for cold water ablutions, and on the other an extended suite with various warm bathing forms, among them especially sweat baths.

Source: wiktionary