Huh. Kinda had a different idea.
In every generation, there are humans or other sapient mortals who are said to be born with Giant Spirits. They, in turn can forge a mental imprint with a giant, becoming a sort of hybrid creature, the human (elf, gnoll, kobold, whatever) is the Guide, who provides the alien intelligence of a giant with the goals and ambitions of an intelligent being, rather than somewhat alien-beast intelligence.
The giant however provides the Body. The Body has needs. Absorbing and relinquishing magic, living around comfortable leylines and manapools, fucking, and so on.
Cities are founded on the back of these Titans because they tend to be safe, as well as the trade nexuses of Kingdoms, the giants being a kind of citadel unto themselves, often enough, brought to a vaguely controllable level with Guides. "Vaguely", mind you, since even as Bodies become more human with the exchange, Guides become more alien, and in then end Guide/Bodies have more in common with other giant-symbionts than the respective races they came from, especially when a Body wants to and eventually does fuck and the other way around.
So, you know. A lot of adventure hooks there. Helping a Guide tame a Body, kingdoms trying to keep a hold of things when their Guide takes a city off to do some unknowable giant thing or something. Wars between different kingdoms on the backs of giants.
Oh yeah, and different types of giants doing different things and whatnot. Rocky giants digging and building mountains and passes, humanoid giants leading flocks and herds of beasts, hybrids doing other stuff, and Guides bonding with all different kinds of giants...