I am on a slow-moving motor launch sailing up the mysterious Acheron River, symbolized in Greek myth as the River Styx. There are no corpses aboard this boat, their eyes sealed shut with gold coins.

The ferryman is not Charon, but a jovial old salt, Captain Kostas, who has kept the passengers entertained as he navigated the boat up the river from the port of Parga. I am on my way to visit the Oracle of the Dead, the Necromanteion, a mystical sanctuary that the ancient Greek believed to be the entrance to the Underworld. Hades!

Captain Kostas moors the boat by a reedy embankment from where the passengers must walk two kilometres to the site. I trudge up the gravel road, through the corn fields to the small village of Messopotamo.

On a hillside behind the village, protected by cyclopeon walls and an inner circuit of polygonal masonry, dark passageways lead to the mouth of an underground cavern which was believed to be the entrance to the realm of Hades and Persephone. Ancients came here to consult the souls of the dead who, on leaving their bodies, acquired knowledge of the future.

The Necromanteion near the beautiful town of Parga on Greece's west coast belonged to the ancient Bronze Age city of Ephyra, the ruins of which are located nearby. The site had been inhabited since Mycenaean times judging from the finding of several shards and a bronze sword dating to the 13th century BC. The labyrinth and buildings, which include store rooms, priests lodgings, dormitories, baths and a courtyard, were discovered in 1958.

The Necromanteion was the most famous sanctuary of its kind in antiquity. Many pilgrims visited there including Odysseus, who attempted to conjure Achilles' ghost. The ancients believed that a person's soul was immortal after its freedom from the body, and that a mortal's contact with the dead, with a view to predict the future, demanded special sacrifices and rituals. Offerings of milk, honey and the blood of sacrificed animals were made in the hope of conjuring the spirits of the departed.

The pilgrims were subjected to three stages of physical and spiritual tests, during which they were isolated in the dark rooms of the Oracle. Obliged to follow a special diet of beans and various hallucinogenic substances, they prepared to meet the souls of the dead.

After several days of magical rituals, prayers, invocations, and questioning by the priests, the supplicants were led down the dark, smoke-filled corridor of the labyrinth to the entranceway of Hades, having faith that the apparitions of the dead would appear to them. An underground vault, thought to be the dark palace of Persephone and Hades, was the meeting place of the dead and the living.

I descend into the cold, musty crypt by a narrow stairway. The chamber is carved in the rock with 15 stone arches supporting the roof. It dates to the end of the 4th century. It is here that the pilgrims were believed to have communed with the dead.

As I stood in the gloom of the stone cavern I try to conjure a few ghosts of my own.

It is an eerie place, not impossible to imagine how the pilgrims, disoriented and under the influence of potions, could be fooled into believing the dead were really there communicating with them.

During Roman times, in 167 BC, the Oracle was proven to be a hoax when pulleys were discovered in the chamber, which apparently had been used to hoist up the priests who simulated the departed and answered the questions of the pilgrims.

The walk through the hallucinogenic smoke of the labyrinth, the isolation and rituals they had performed during their stay, prepared them for accepting the appearance of the "dead" person as "real." After this discovery, the Necromanteion was destroyed and lay hidden until it was excavated in 1958 and restored by the Archaeological Society of Athens.

After visiting Hades, I board the launch to return to Parga, cruising downriver to the Acheron delta, then out to the open sea. A brisk wind has blown up and Captain Kostas navigates the boat through the choppy water sailing precariously close to the rocky shoreline. Great jagged rocks loom out of the sea like giant sea monster's teeth. The limestone cliffs are riddled with caves where pirate ships used to hide.

We sail past secluded coves with dazzling turquoise water, stopping to anchor at one of the pristine white-sand beaches, to spend the afternoon luxuriating in Paradise until it is time to board again and head back to Parga.