One of the elements of Ancient Greek society that was the most varied was the gymnasion. Originally a place for physical activity, it became a meeting place for intellectual pursuits as well.

The Greeks did their exercise and sporting activities nude. The word gymnasion comes from gymnos, the Greek word for unclothed. Gymnasium is the Latin version of gymnasion.

The first gymnasia, dating to the 6th Century B.C., were outdoor areas like a wooded grove or an open space next to a river or a spring. Gymnasia were often found at sanctuary sites.

Warfare was common in the Greek world, and gymnasia would have served as training grounds for young men priming for battle. Archery, spear wielding, and javelin casting would have been familiar gymnasion activities.

Nonmilitary sporting activities would have included boxing, jumping, running, and wrestling.

Cities as well had gymnasia, and many of these were enclosed buildings. Athens had a couple of famous gymnasia, Plato's Academy and Aristotle's Lyceum. These offered young men opportunities to learn and discuss literature and philosophy as well as pursue athletic activities.

In Hellenistic times, a gymnasion was a popular destination for larger numbers of men, young and old. Managing a gymnasion was a gymnasiarch, who had the power to approve or dismiss members and impose fines or punishment to transgressors. A trainer employed by the gymnasion was called a gymnast.

As more and more men attended activities at gymnasia, the buildings expanded further, to include exercise-related elements like washrooms, bathtubs, and massage rooms. Some buildings contained covered walkways and other areas designed to accommodate training in inclement weather. 

A dedicated running track accompanied some gymnasia. Some of the larger gymnasia were complexes of buildings, including a stadium. The Asia Minor city of Pergamon contained one of the largest gymnasia ever built; it measured more than 320,000 square feet.

The Greek gymnasion served as the basis for many a Roman bath.