Roaming the halls, you can almost sense it's sinister past. During World War II. It was a laboratory, and the scientists were chemical weapons specialists -- experts at human suffering.
To get here, I took a ferry to a tiny island called Okunoshima, the perfect location for a secret operation.
So who would come to this tiny place with such a dark past? People who are fascinated by ... rabbits.
Within steps of dry land, little bunnies will greet you without hesitation. The island is no longer a place of misery, but instead, provides enormous joy.
Thousands of friendly, fearless, adorable rabbits live here.
If you enjoy the attention of these soft furry fellas, this island will give you that "nowhere else on Earth" experience.
What's unique about this island is there are no predators. There are no coyotes, no bobcats, nothing that's going to eat a rabbit. So when people show up, the rabbits come right up to you, especially if you have something to feed them.
When the war ended, the chemical weapons lab closed down and released all the lab rabbits into the wild. Since there are no predators, they simply multiplied, living in perhaps the most rabbit-friendly environment in the world.
Masanori Kurosaki, who works at a museum on the island, says during the war, 4,000 to 5,000 people lived on the tiny island, manufacturing chemical weapons.
Today, no more than a dozen people live here. This is rabbit island now.
People like Makiko Tokuyama from Osaka visit the island to soak in the experience.
"It's beautiful," she said.
And Ekway Karauchi is a frequent visitor. She says she loves rabbits and says this is their paradise.
Seventy-five years ago, the island was once a place with cruel intentions. As the saying goes, out of darkness comes light, and out of that light comes hope.
Perhaps this island represents something more than a happy place for bunnies.
If you ever want to visit the island, it actually has a small hotel. And a tip, the rabbits love fresh vegetables, so if you bring some, you will have no problem making friends.