The stadium at Olympia, shown in this image, was the site of the first Olympic games in 776 BCE. It held about 50,000 spectators.
The games were contests between representatives of various Greek city-states which were often at war. This made travel between them dangerous.
So messengers were sent out announcing a 'sacred truce' lasting for the month before the Games began so that contestants and spectators could travel to Olympia in safety.

The games were held in honor of Zeus, King of the Greek gods. Originally the temple at Olympia held a large cryselephantine (ivory and gold) statue of Zeus sculpted by Phidias
who made the Pediment sculptures of the Parthenon and the enormous cryselephantine statue of Athena for the Parthenon.
The monumental statue has long since been lost, though it is known from images on coins of the time.
It is considered to be one of the 7 Wonders of the Ancient world.

Only men were allowed to participate in the games, and all the races and various contests were in the nude.
Only men, boys and unmarried girls were allowed to attend the Olympic Games. Married women were not allowed into the Olympic Games.

At the beginning, the Olympic games only included a race from one end of the stadium to the other.
Over the years, more events were added , increasing the games to four days of competitions.
Some of the events were wrestling, boxing, long jump, javelin and discus throwing, and chariot racing.
One of the most difficult events was the hoplite race where men raced wearing armour and carrying shields.

This picture shows several groups of tourists at the site, and frequently some of the groups have
their own "Olympic games"... fully clothed though.