The secret hiding inside the Rock of Gibraltar

When you think of the Rock of Gibraltar, you might think it's just a formation of — well, rocks. But this politically important island hides more than you can imagine. Inside the Rock of Gibraltar lies a maze of tunnels. Tunnels that became of great importance for the British during World War II and marked the Rock, as it's sometimes called, as a staging area for troops.

The Rock of Gibraltar sits on the territory of Gibraltar in the Iberian Peninsula. According to the BBC, the British have ruled over Gibraltar since 1713. The territory looks a lot like many British towns, wrote The Guardian, with familiar department stores and restaurants. Its inhabitants have staunchly resisted shared sovereignty between Spain and the United Kingdom. Gibraltar has such a small-town feel that you'd never know it was a strategic location during the war.

Dominating the island is the Rock of Gibraltar, which looks like a huge mountain. It has caves and massive cliffs that look imposing. But the British soldiers knew it wasn't enough. The Rock could also help them hide. The British army began digging tunnels into the geological formation, augmenting the natural tunnels that exist, reported Atlas Obscura. Then they opened up a 45x16x8 feet hole dubbed the "Stay Behind Cave" as the site of a top-secret plot called Operation Tracer.

They were going to hide in a cave for a year

The tunnels inside the Rock of Gibraltar were not new. Culture Trip explained that the tunnels were first dug in 1782. They served as an underground roadway for British soldiers to move around and spy on the Spanish and the French troops trying to take Gibraltar. By World War II, the British army extended the tunnel system by another 18 miles. According to the Gibraltar website, the tunnels provided protection from air raids. The tunnels had street names so people wouldn't get lost. They built bunkers for lodging and food storage. Workshops were set up to repair vehicles. There's even a bakery.

The tunnels were so massive that the "Stay Behind Cave" was not discovered until 1997, wrote Atlas Obscura. The British government, afraid that Gibraltar might still fall onto the hands of the Axis powers despite its massive tunnels, wanted to ensure they had spies on the inside, literally. So they started Operation Tracer. They dug the cave where six men would stay with a year's worth of equipment, including radios and generators. The plan was to report on German movement if the island fell.

Fortunately, Operation Tracer was never invoked. The chamber was then closed off. Over the years, people tried looking for the "Stay Behind Cave" until a team of explorers found it. These days, tourists can roam around the secret caves and tunnels. The Rock of Gibraltar: not just a rock after all.