New New York Undercity
From Tardis Wiki, the free Doctor Who reference
The Undercity of New New York was the poverty-stricken lower levels, built underneath the main city of New New York on New Earth. It was linked to the other levels via the Motorway.
It was filled with slums in the alleys, known as Pharmacytown, where pharmacists sold mood drugs. However, the mood drug Bliss did not reach the Undercity, allowing all the people inside to survive and later repopulate the upper levels. (TV: Gridlock)