The Recreo Verde tourist complex in Venecia de San Carlos, Costa Rica, is home to a tiny mountain cavern that has come to be known as The Cave of Death due to its ability to kill any creature that enters it.

Located on the edge of the Poas Volcano, la Cueva de la Muerte is only 2 meters deep and 3 meters long, which makes it a seemingly cozy refuge for insects, birds, and small animals looking for shelter. But appearances can be deceiving, as entering this tiny cavern results in an almost instant death. Although the tiny cave looks harmless to the naked eye, it is filled with carbon monoxide, a colorless, odorless, tasteless gas that also happens to be extremely toxic. To demonstrate just how lethal the Cave of Death actually is, local guides place a lit torch inside the cavern and it is extinguished instantly by the absence of oxygen and the high concentration of carbon dioxide.