The tunnel of Eupalinos is currently a widely known and visited archaeological site in Samos, managed by the 21^st Ephorate of Prehistoric and Classical Antiquities of the Ministry of Culture. It was designated as an UNESCO World Heritage Site, along with Pythagoreion, in 1992.

Today, only a part of the tunnel is accessible. To enter, the visitor goes through the 1882 stone building at the southern entrance and finds himself in front of a discomfortingly narrow, rectangular opening in the floor. A steep flight of descending steps leads to a narrow walled passageway of elaborate masonry and pointed roof, about 12 meters long. The visitor then enters the tunnel, illuminated by electric lights, for about 300 meters. Further access is discouraged for health and safety reasons.

A recent study of 2011 to render the site visitable from one end to another passed the Central Archaeological Council control, and awaits for its implementation.  

Admission information could be obtained here (Link).

 Eupalinos achieved for the first time in the history of humanity to construct such a work. He organised and executed his plan with absolute precision. … Now we feel obliged to restore and make known this master piece and offer it to the public as it should be because it belongs to the world heritage. 

(Tokmakidis, 2011)