View of the interior to the Tunnel of Eupalinos that brought water to the ancient city of Samos (now called Pythagorio). The outline of the rock-hewn tunnel is very clear in this image. The woman in the picture is 5' 2" [1.57 m.] tall.
The area in which she is standing was actually a "service area" that was used by workmen to maintain the tunnel. The metal grating behind her, on the left side of the image, covers the deep channel in which the water actually flowed.
The tunnel was about 3,280 ft. [1,000 m.] long and was carved in solid rock by two groups of workmen—one group beginning at each end and meeting near the middle. It was completed during the rule of Polycrates around 524 B.C.
It is interesting to compare "Hezekiah's Tunnel" in Jerusalem that was dug by two gangs of workmen—also digging from each end toward the middle. Hezekiah's tunnel is only 1,760 ft. long and was probably constructed in the late 8th century B.C.