New light is being shed on a mysterious network of tunnels and caves carved out of rock underneath Scotland's capital Edinburgh, the media reported on Friday.
Scientists from the universities of St Andrews and Edinburgh are now using radar imaging equipment have discovered the ancient passageways at "Gilmerton Cove" extend much further than originally thought, the BBC reported.
More chambers have also been uncovered during the research project.
The caves lie under the former mining village of Gilmerton in the south of Edinburgh.
Simon Shackley, from Edinburgh University's School of Geosciences, said: "On the other side of Gilmerton Road there is a rather large chamber that is probably about 4 metres deep."
"There also appear to be cavities in front of the cove and behind it - both about 2 metres deep".
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According to experts, the underground passageways and chambers contain stone benches, tables and even a small chapel hand-carved out of the sandstone.
The network has been linked to druids, witchcraft, a gentlemen's drinking den and even Mary Queen of Scots.
Richard Bates, of St Andrews University, told the BBC that the tunnels were "strange places" with very little detail about who used them or why they were built in the first place.
"Perhaps by the work we're doing - if we're getting a bigger picture we're mapping in a more extensive way the footprint of it - then what we're hoping is that will tell us something about the use," he said.
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