The Dragons of Babel

A war-dragon of Babel crashes in the idyllic fields of a post-industrialized Faerie and, dragging himself into the nearest village, declares himself king and makes young Will his lieutenant. Nightly, he crawls inside the young fey's brain to get a measure of what his subjects think. Forced out of his village, Will travels with female centaur soldiers, witnesses the violent clash of giants, and acquires a surrogate daughter, Esme, who has no knowledge of the past and may be immortal. 

Evacuated to the Tower of Babel--infinitely high, infinitely vulgar, very much like New York City--Will meets the confidence trickster Nat Whilk. Inside the Dread Tower, Will becomes a hero to the homeless living in the tunnels under the city, rises as an underling to a haint politician, meets his one true love–a high-elven woman he dare not aspire to.

You've heard of hard SF: This is hard fantasy from a master of the form.