Deep underground, the Nazis built a city for thousands of soldiers. Now it’s a tourist attraction

The countryside around the little Polish village of Pniewo looks serene, with its yellow crops and patches of forest, but beneath the surface lies a sprawling 20-mile maze of tunnels, shafts, underground railway stations and combat facilities. (Simona Murrone/Archaeological Park of the Colosseum via CNN Newsource)

In our roundup of travel stories this week: the seven-foot “monster” that stalked West Virginia, the Roman tunnel where a hated emperor nearly met his end, and the enormous bunker city built by Nazis in central Europe.

Poland’s Nazi labyrinth

The countryside around the little Polish village of Pniewo looks serene, with its yellow crops and patches of forest, but beneath the surface lies a sprawling 20-mile maze of tunnels, shafts, underground railway stations and combat facilities.

This is the Ostwall, a fortified subterranean complex built by the Nazis and abandoned in 1945. In the 1980s and ‘90s, a subculture known as the Bunker People took over the tunnels, hosting unauthorized and often dangerous events here, from raves to weddings. Today, bats are its inhabitants, some 40,000 of them taking refuge in the darkness.

In the 21st century, it’s been given new life as a dark tourism destination, with 19 miles of tunnels open to explore in the Międzyrzecz Fortified Region Museum. Read more here.

Rome’s murder-plot tunnel and London’s Cold War spy maze

In Italy, a 2,000-year-old tunnel once used by Roman emperors to slip unseen into the Colosseum will open to the public this month. The 180-foot Passage of Commodus takes its name from Emperor Commodus, who you may remember as the conniving meanie portrayed by Joaquin Phoenix in “Gladiator.” Experts believe he once survived an assassination attempt here. He would later meet his end being strangled by a champion wrestler.

Fans of secret underground complexes will have much to celebrate when The London Tunnels opens in the UK capital, with a speculative date of 2028. This mile-long series of chambers was built to shelter citizens in World War II, before becoming the home of Britain’s Special Operations Executive, an offshoot of MI6 and the real-life inspiration for James Bond’s Q Branch. It’s undergoing a $149 million transformation in hopes of becoming the city’s grandest new tourist attraction. CNN went down below for a sneak preview earlier this year.

Turkey’s ghost town and Iraq’s lost city

Just over a century ago, Kayaköy in southwest Turkey was a bustling town of more than 10,000 people. Abandoned by its occupants and haunted by the past, it’s now a ghost town, a physical reminder of darker times following the Greco-Turkish war.

Its crumbling buildings swallowed by greenery are starkly beautiful and deeply eerie, even more so as the cooler seasons creep in and sea mists descend. Today’s visitors pay a three-euro fee to wander its uneven lanes and alleyways. Here’s what CNN discovered on its visit.

Babylon, in modern Iraq, meanwhile, was the jewel of Mesopotamia and one of the most important cities in antiquity. Today, its ancient ruins are a site in distress, its paths overgrown and facilities scarce. But when the late afternoon sun hangs heavy over Hillah, its steps and statues bathed in heat and light, visitors still feel that they are standing in the footprints of kings.

America’s most haunted

The Trans-Allegheny Lunatic Asylum in West Virginia looks like the asylum of nightmares and for many, it was. But it started out as a place of compassion whose massive overcrowding led to desperate measures by doctors and staff. Daily and nightly tours now offer visitors its complex history, along with an occasional paranormal scare.

Many former asylums are now macabre tourist attractions, whose treatment of their subject matter can range from the sensitive to the sensationalist. CNN delved deeper into the surprisingly hopeful history of asylum tourism in America.

Maureen O’Hare, CNN