An ancient "tunnel-like" structure has been unearthed in the garden of the General Post Office in the Indian city of Mumbai (Bombay).
The authorities say it is clear that the previously undiscovered structure is not a sewage or storm-water drain.
It was only revealed when a local newspaper reporter asked to see it.
The heritage committee is yet to inspect it, or decide what exactly the structure is. Experts say such tunnels were often part of fortified basements.
The post office was built 97 years ago.
Chief Postmaster General Faiz-ur-Rehman told the BBC that the discovery of the structure came as a surprise.
"I have been here for more than 20 years," he said, "but was never aware of its existence.
"When we managed to open it there was no foul smell. We have called in the experts now and they will establish whether it connects anywhere else."
Some reports say there is a possibility of it being an escape route connected to another tunnel.
Three ways out, with covers, have been found so far in the garden.
Director of Postal Services Abha Singh said that the covers had holes in them, indicating they were not conventional manholes.
"It was perhaps to allow air to pass so that people did not suffocate. If it was just for sewage then the lids would be closed completely," he said.
Mr Rehman said that the original drawings for the building were not available in India.
Officials say they could be in the UK - the former colonial power.
"Maybe if we could access the original plan we may be able to find out if there are more - and what purpose these structures served."
Officials say that if the history of the tunnel is confirmed, they could try to win a higher heritage grade so the structure could become a tourist attraction.
"Unless an architect or engineer investigates further it will be difficult to say if it is a huge basement or a tunnel," historian Sharada Dwivedi said.
"Tunnels were common to forts - whether it was Maratha, Mughal or British forts."