A retired engineer from Swansea is campaigning for ancient burial sites to be considered sacred ground.
The skeleton was buried in the cave around 26,000 years ago
Chris Warwick, who is now a druid, said places like Paviland cave on Gower should be treated the same way as modern graveyards.
A skeleton, about 26,000 years old, was discovered in the cave in the 1800s and dubbed the red lady of Paviland.
Mr Warwick is setting up a group called "Dead to Rights" to work for the return of remains to such sites.
The druid is spending the weekend in the limestone cave to highlight his cause and to try to "balance the spiritual energies".
"Our feeling is that it isn't just modern graveyards that should be considered as sacred sites, but anywhere that a body has been buried with ceremonial intent," he said.
"We have formed a little group called Dead to Rights, to work for the return of remains to the sites they were buried in and hopefully have them reburied there with due ceremony.
"The sites would be regarded as sacred thereafter."
Mr Warwick told BBC Wales there were plenty of sites across the world where bodies had been buried in pre-historical times.
He said he had decided to sleep in the cave so he could get in touch with the ancestors and find out what was "amiss" with the burial site.
"There's obviously going to be something amiss since the bones and the grave goods have been removed. [I] then try to do what I can to alleviate the balance.
The remains of the red lady of Paviland were discovered by palaeontologist and clergyman Reverend William Buckland, who removed them from the cave.
Rev Buckland mistakenly assumed the skeleton was female - as it was dyed red - and dated back to Roman times.
It has since been identified as a man and many thousands of years older.
The skeleton was taken to Oxford University, where it remains.
The Dead to Rights group believes the removal of the bones was a "desecration" of a sacred site and says they should be reburied in the cave or nearby "with due reverence".
Mr Warwick said he was happy for archaeologists to photograph and examine burial sites.
He added: "The more we find out about our ancestors the better, as far as I'm concerned. What I do object to though is the grave robbing that goes on - whichever way you put it, that's what it is."