The entirety of the initial background for a possible Underworld, to be run in an as-yet unknown venue using either 3LB or B/X:
His Incomparable Effulgence the Dread High Dingus of the Great City of Faz has decreed that the Underworld beneath the City is open for plunder, its denizens to be regarded as caitiffs and malefactors utterly without recourse to the otherwise boundless beneficence of the law.
You have consulted with a hooded figure in a soggy reeking tavern, the consensus being that information thus gleaned is unimpeachable in such matters. His sibilant counsel is that one ingress to the maze lies in the Furtive Quarter, in the cellars of the ruined Temple of Ghonk. And that is where you, suitably outfitted and girded, find yourselves.