A cave hidden beneath an 11th Century castle in Pembrokeshire is a "truly remarkable site" which could rewrite Britain's prehistory, researchers say.

Small digs of the cave under Pembroke Castle, known as Wogan Cavern, have so far uncovered "extremely rare" evidence of early humans and animals - including the bones of a hippopotamus which roamed Wales 120,000 years ago.

The University of Aberdeen will now lead a larger five-year exploration of the site, which archaeologists hope could reveal "a great deal about our early prehistoric forebears".

"There is no other site like it in Britain โ€“ it is a once in a lifetime discovery," said Dr Rob Dinnis from the University of Aberdeen.

Wogan Cavern, thought to have been dug out by the Victorians, is accessed via a spiral staircase from the castle.

Measuring 23m (75ft) in length, with a height of up to 10m (32ft), the cave has been described as "enormous".

It was long assumed that there was little archaeological material left at the site, but small excavations between 2021 and 2024 uncovered evidence of both humans and animals over more than 100,000 years - including stone tools and mammoth, hippo and woolly rhinoceros bones.

The bones have been described as well preserved, and researchers said the cave was emerging as one of the most important prehistoric archives in Britain.

Dinnis, who directed the initial digs and will lead the new excavation project, said he was optimistic about what they would uncover.

"Despite the limited work done so far, we can already say that Wogan Cavern is a truly remarkable site," he said.

"Not only is there extremely rare evidence for early Homo sapiens, there are also hints at even earlier human occupation, probably by Neanderthals.

"There is no other site like it in Britain โ€“ it is a once in a lifetime discovery. With this new project we can learn a great deal about our early prehistoric forebears, about how they lived and what their worlds looked like.

"We are optimistic that the cave can chart a long sequence of human activity, from hunter-gatherers living there immediately after the last Ice Age around 11,500 years ago, back to Britain's earliest Homo sapiens between 45,000 and 35,000 years ago, and maybe also earlier traces likely left by Neanderthals.

"We have also found hippo bones, which probably date to the last interglacial period, around 120,000 years ago. The site could therefore tell us about how multiple changes in climate and environment affected people living there over 100,000 years or more."

The university will lead on the exploration supported by the Pembroke Castle Trust, which said the finds from Wogan Cavern would be curated and kept in Pembroke.

For Pembroke Castle โ€“ the birthplace of Henry Tudor and a popular tourist attraction โ€“ the project represents an exciting new chapter in its history.

"This is incredibly exciting news for everyone at the castle," said manager Jon Williams.

"We have watched with great interest as Wogan Cavern has started to reveal its secrets โ€“ it's very different from the medieval history we usually deal with at the castle."

The new excavations are scheduled to begin at the end of May.

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