The story begins with the explorers arriving at an island characterized by dusky green forests and ancient, decaying buildings visible from afar. As they ascend the foothills, they encounter traces of ancient roads and ruins that become more prominent as they climb higher. Eventually, they find an ancient road that leads them up a cliff to a plateau, where they are astonished to discover the remnants of a phantom city. This city, seemingly abandoned and ghostly, consists of stone houses and a colossal, metallic pyramid that dazzles in the sunlight.

Exploring the city, they find no signs of life but are drawn to the central pyramid, which seems to be made of a strange, untarnished metal. Exhausted, they sleep on the pyramid's altar-like pinnacle and awaken at dawn, eager to explore more of the island. Their journey takes them to the southern slopes, where they find a large cavern that evokes a strange sense of familiarity in both men.

Inside the cavern, they discover the skeletal remains of two ancient warriors, each bearing signs of a violent end—a flint dagger and a bronze sword. These findings unsettle them deeply, stirring inexplicable memories and sensations. The explorers are compelled to leave the cave, driven by an eerie compulsion and mutual recognition of the ancient artifacts.

Continuing their exploration, they stumble upon more ruins covered in hieroglyphics, which the Dutchman recognizes from his studies with a Professor von Kaelmann. He identifies the writings as Lemurian, relating to a legendary civilization older than Atlantis. As they venture further, they come upon another grand temple, seemingly well-preserved and exuding an aura of ancient power.

The temple's doors, initially smooth, reveal horrific carvings of a monstrous skeleton when scrutinized. The explorers manage to open the doors and enter the vast, dark interior filled with colossal columns and a sense of malevolent presence. Ascending a seemingly endless staircase, they reach a platform with an enormous anthropomorphic figure and an altar. A near-fatal encounter with a moving statue convinces them to flee, clutching a white cylinder they found on the altar.

Their flight from the temple is marked by a bizarre distortion of time, as they find the day has turned to dusk upon their exit. Overwhelmed by fear and the uncanny experiences, they hastily descend the hill slopes, leaving behind the enigmatic and terrifying relics of the lost Lemurian civilization.