The Tunnel of Eupalinos lies just outside Pythagorion on the island of Samos. Built in the 6th century BCE, it once served as the city’s main aqueduct. The engineer Eupalinos of Megara designed the tunnel to carry fresh water from a spring to the ancient city. Today, it stands as one of the most impressive examples of ancient engineering in the world.

Unlike many ancient structures, the tunnel shows advanced planning. Workers dug from both ends and met with striking accuracy in the middle. As a result, the tunnel stretches over 1,036 meters through Mount Kastro. 

In terms of size, the tunnel averages 1.8 meters in both height and width. However, some sections narrow to just 1.5 meters in height and 0.42 meters in width. Inside, conditions remain constant. The temperature holds around 16.5°C, and the air feels humid. Therefore, visitors should wear sturdy shoes and move carefully, as the floor may be damp and uneven.

Visitors can choose between three different tour options. First, Route 1 offers a short, 185-meter walk. It introduces guests to the tunnel’s basic features. Next, Route 2 extends 424 meters and includes a Byzantine-era cistern and the exact meeting point of the two digging teams. Finally, Route 3 runs the full 1,036 meters. This route ends at the original spring in Agiades and suits more experienced explorers. However, this longer tour requires advance planning and transportation back from the exit.

Furthermore, the site follows strict visitor rules. Only those aged 14 and above may enter. Anyone under 18 must have adult supervision. Helmets, provided at the entrance, are required for safety. Large bags are not allowed. While visitors may take photos, flash and professional equipment need special permission.

The Tunnel of Eupalinos forms part of a UNESCO World Heritage site. Alongside the Pythagoreion and the Heraion of Samos, it showcases the island’s rich cultural history. Moreover, the tunnel functioned as a water system for over 1,000 years, making it one of the longest-serving systems of its kind.

In conclusion, the Tunnel of Eupalinos combines historical depth, technical brilliance, and unique visitor experience. Its preserved structure offers rare insight into early engineering. For this reason, it remains a must-see destination for anyone traveling to Samos.