George Kourounis stood at the edge of a red-hot lava lake, fiery molten rock gurgling just feet away as caustic acid rain splashed his protective suit.

It was a "window into hell," he said. "Dramatic and violent."

Kourounis is an explorer and documentarian, and last month, he and Sam Cossman, an explorer and filmmaker, dived deep into the Marum crater, located in an active volcano in the archipelago of Vanuatu in the South Pacific -- and the fearless duo brought cameras in with them to capture their momentous adventure.

(Watch the astounding footage, posted online this week by Cossman and taken with a GoPro, as well as with a Canon 5D Mark III camera and a Sony NX Cam, in the video above.)

"Going down into the crater of Marum has been a dream of mine for many years," Kourounis told The Huffington Post via email. "It was exhilarating, to say the least."

Kourounis, Cossman and two guides, Geoff Mackley and Brad Ambrose, spent four days on the volcano and descended twice into the crater. According to Kourounis, the descent was a whopping 1,200 feet. That's "about as deep as the Empire State Building is tall," he said.

A documentarian who specializes in capturing extreme forces of nature, Kourounis -- who has chased twisters and even got married at the edge of an exploding volcano -- is no stranger to extreme adventure and danger. But the journey into Marum, he said, was one of the most intense experiences he's ever had.

"Getting to [Marum] was kind of like a reverse climbing of Everest," he said. "The volcano fought back at us, and we had to deal with terrible weather, tremendous heat from the lava, descending and ascending 400 meters of near vertical, loose rock face, acid rain so strong that it could have come from a car battery, and a variety of other craziness."

Kourounis says he got so close to the lava that splashes of it melted a hole into his rain jacket and also a part of one of his cameras.

"When you see that shot of me [in the video] looking like a little silver dot, next to what appears to be a waterfall of lava, that was an extremely dangerous spot to be standing," he said. "It was a bit scary. If something were to have gone wrong. It would’ve happened quickly, and catastrophically."

Cossman told The Huffington Post that though the experience was terrifying, all fear was "eclipsed by a surplus of adrenaline when dangling above the nearly unimaginable, sight of a glowing fiery pit likened only to the surface of the sun at close range."

"Undoubtedly, this experience was the pinnacle adventure of my life," he said.

It was an "amazing expedition," Kourounis added.

We bet it was.