Vaults of ambition: shock find under London Museum enchants its builders

Discovery of Victorian network hiding under some of city's busiest streets set magical' new challenge for 150m project

When a contractor working on the site of the new London Museum at Smithfield market knocked a tentative hole in a bricked-up basement wall, all he could see, peering in with a torch, was a muddy pile of rubble and some scurrying rats.

That unpromising beginning, however, would lead to an unparalleled" discovery. Behind the wall, once the detritus had been carefully removed, the architects and builders were astonished to find an enormous and beautifully constructed network of subterranean brick vaults that no one, even a year into the ambitious multimillion-pound building project, had known were there at all.