Ardhata, a fantasy MegaCity and MegaDungeon

For the past month or so I've been kicking around an idea in my head of a campaign based in a huge fantasy city, over the ruins of a megadungeon.  The campaign would incorporate classic dungeon crawls but also some of the ideas for city crawls that I've seen thrown about in the OSR community. Also... dinosaurs, psionics, airships and the risen Old Ones.

Ardhata sprawls across the southern edge of the Great Barrier Plateau, far from the world-splitting horror that is the Crack of Night.  Its original builders rose and fell as a civilization far into pre-history.  Adventurer-scholars tell of carvings of these builders at the deepest levels of the Undercity, their faces long since defaced by some unknown vandals.  The original city was sited at a spot where the sheer and monumental cliffs of the plateau gentled into a vast and rolling slope down to the edges of the Vurdid Jungle which laps at the base of the plateau's cliffs as a sea of fecund green for hundreds of miles to the East and West.  The first builders constructed the city as a series of vast and gradual terraces that reached from the edge of the jungle to the South and to the fertile grassland of the upper plateau in the North.  Since those first builders, a succession of races have claimed the city, each one building upon the ruins of the last until conquest, disaster or stagnation bring their downfall.

Today the city is ruled primarily by the races of men, but a myriad of other races call the place home.  Ardhata has always been a large city and a major trading hub for all of the South and of planes beyond.  Since the fall of Xoan and the opening of the Crack of Night, Ardhata has become the largest city on the continent.  The original city of once gentle terraces is gone and a new city lies atop the towering ruin cliffs.  From the Vurdid Jungle, one can gaze upward at the layer upon layer of eldred architectures that lie sandwiched below the current city.  Ardhata is criss-crossed by many chasm-canals that reach down into darkness and the very lowest levels.  The largest canals are hundreds of feet across, but many smaller canals can be found in back alleys, some only an arm span across and choked with junk.

Rumors about Ardhata

Some say the giant statues that the slum known as the Pedestal District is built on contain secret entrances to stairs that wind straight down to the lowest levels of the city.

The Undercity Adventurers Guild has recently discovered a formally unexplored section of the Undercity but are using any means necessary, including assassination to keep its location a secret.

A contingent of tall insectoid wizards has taken up residence in a rented palace.  Some fear they are the original builders, returned from exile among the starts.

Gray Sphinx by oukamiyoukai45

An sphinx envoy from the Echidnae Empire is visiting at court, seeking an audience with the Gray Prince.

The price of saurian meat rises higher and higher every year and the peasant rumbling is getting dangerous.  Dinopokes no longer venture into the poorer parts of the city.

The secretive Cult of the Gilded Eye have recently opened an orphanage.  That can't be good.

The size and territory of the Wet Mouth gang is growing at an alarming rate.  The bodies of rival gang leaders are being found in increasingly gruesome states.

City engineers say the Red Market District is sinking.

The Society of the Cistern has been gaining more and more influence in the court of the Gray Prince.

A swarm of giant corpse roaches erupted from the Moss Chasm of the Artificers' District last week.  What could have driven these subterranean creatures into the light of day?