The 2,000,000-year-old Koutouki Cave was mapped in 1954 by the Greek Speleological Society. It is one of the most beautiful caves in Attica and stands at an altitude of 510 meters above sea level. It owes its creation to the karstic phenomenon of Mount Ymittos and its final form was affected by earthquake activity.

Koutouki is a vertical cave with an artificial entrance in the form of a 17 m long tunnel, while the natural entrance is a crack in the bedrock caused by tectonic movement at the roof of the cave which is 38.5 m high. It has an underground route of 350 m and consists of a single chamber of 60 x 60 m with rich rock decoration of stalactites and stalagmites and the unusual coloring of various speleothems.

A number of oxides along with water create an unusual coloring and rock formation that resemble sculptures. Rust red from iron deposits penetrate the inner rocks and create a red waterfall, while other rocks resemble a horse or a dragon. The temperature of the cave is 17°C and the humidity is 90%, while fauna is very sparse due to human presence and the continuous exposure to light. Notably, the tour of the cave is enhanced by the use of sound and lights.

Since the early 1960's the cave has been an attraction pole for many visitors due to its natural beauty and close vicinity to the city center. Thus, it was developed by the Hellenic Tourist Organization (EOT). Today, the management of Koutouki is overseen by the Hellenic Ministry of Culture.