A 200-year-old tunnel has been unearthed by the workers of the General Post Office GPO in its compound at south Mumbai's Chhatrapati Shivaji Terminus. According to GPO workers, the tunnel that resembles a dark cave-like structure has a vast hall, thick walls, pillars, muddy floor and unidentifiable plants with pretty flowers among other things.The discovery of this tunnel was made on Friday, after a newspaper reporter learnt about the place and informed GPO authorities to check it.Postal Services, Director, Abha Singh said that for decades the flag-hoisting ceremony is conducted at this spot but it was never known that there was a tunnel. The lid was believed to be a drainage cover until few workers lifted them and found ladders running down.