In 2017, newly published Land Registry data revealed 4 million km of networks and telecommunications lines underneath London, many of which were secretly constructed by the Post Office, British Telecom and the Ministry of Defence. These mysterious Cold War-era tunnel systems and underground chambers, which number in the hundreds, have been a source of fascination for decades. Yet, until recently, authorities remained conspicuously secretive about them, many owned by the Ministry of Defence and never publicly acknowledged. The most intriguing revelation was of the Postmaster General's secret tunnel beneath the heart of the government at 57 Whitehall. More than 30 gears and a dozen lifts " stretching from the working-class East End to the heart of Whitehall " connect the Postmaster General's tunnel to a secret underground network, which mostly emerges unobtrusively into government buildings and telephone exchanges. Further, a short distance from Whitehall, an A-bomb-proof telephone exchange deep underneath High Holborn street " originally built as a deep-level government air raid shelter in the early 1940s " was a top-secret hub of more than 200 engineers from the 1960s to the '80s. The two-tunnel shelter was extended by the addition of four tunnels at right angles to the originals to become the termination point of the first transatlantic telephone cable, and was spacious enough to boast a staff restaurant, tea bar, games room and licensed bar.