First diver to explore inside an iceberg shares terrifying experience of almost not making it back out alive

Thanks to the real-life disaster that inspired the Titanic movie, generations of us have been raised with a vague fear of icebergs.

These huge hunks of ice are famous for having far more mass hidden underwater than you can see from above sea level, and being so massive that they can easily carve holes in ships.

But there are some people out there who see and hear all that and just can't resist the urge to get up close and personal with an iceberg.

The perfect example is Jill Heinerth, a professional diver and underwater filmmaker, who can now lay claim to the title of the first person to ever dive inside an iceberg.

She managed the death-defying feat back in 2001, exploring the B-15 Iceberg in Antarctica, a floating island of ice roughly the size of Jamaica.

She explored the iceberg with two others, diver Paul Heinerth and underwater cinematographer Wes Skiles, and all three encountered plenty of issues during the ambitious expedition.

When they finally got into the depths around, below and through the iceberg, they found a completely otherworldly series of sights.

Heinerth described the experience in a diary piece for Boston-based publication WBUR, and said that after swimming down through a massive fissure in the iceberg, they reached the sea floor, finding it absolutely swarming with life.

From small filter-feeding organisms to strange isopods that she said were "kind of like something between a spider and a lobster", and even more horrifyingly "started raining down from cracks over my head and crawling along the floor and hitting my camera and landing on my shoulder. It was like horror story material."

Things really got scary when Heinerth and her team started to retrace their path, back through tunnels and up fissures that they'd used to go through the iceberg.

Paul Souders / Getty

When they got to the crack they'd first come through, they found it blocked.

It took them a while to approach the collapsed ice that seemed to be blocking their way, and then slowly pick through it to find small pathways that were still open.

Eventually, they were able to make it through unscathed, and then take a break to acclimatize.

Amazingly, Heinerth described how at this point she could see through to the surface and her boat, where the rest of her team was visibly celebrating that the divers had made it back.

As she recounted: "They told us about what it was like when that iceberg calved and that big chunk of ice sloughed off and closed the doorway and sent this great wave almost capsizing them in the Zodiac [boat]. It was terrifying for them. And the whole time, they were waiting and waiting and waiting and not knowing if we were alive or dead."