Don't change gravity, change the materials it acts upon.
Gravity is not actually the evil illuminatus depriving us of giant animals, machines and buildings, because gravity doesn't feature in the square-cube law at all; it's purely a geometric principle describing how doubling the linear size of an object squares its surface area and cubes its volume and hence (assuming constant density) cubes its mass. The symptoms of this that prevent our exciting creations are many and varied:
- Doubling the thickness of a steel girder squares its tensile strength but cubes its weight, so there comes a point where larger buildings cannot be built strong enough to withstand the forces acting on them. Gravity is one such force, but winds, earthquakes and even solar heating would also take their toll.
- Since insects oxygenate their bodies through direct gas diffusion from spiracles on the surface to a network of tracheae leading to internal organs, their maximum size is constrained by the rate of gas diffusion: doubling their size gives four times as many spiracles but eight times as many cells to nourish
- The maximum height, speed and range of any flying object, be it dragon, bird, plane or rocket, is constrained by the amount of fuel it can carry. Doubling the size quadruples the object's air resistance and octuples its inertia, leading to poor handling and limited range even ignoring the effects of gravity.
In all these cases the problem is that increasing the size increases the beneficial quantity but increases the disadvantages faster, meaning that eventually you reach a limit point where further increasing the size makes the object less effective, not more. In order to truly escape the tyranny of gravity (and all those other forces), therefore, you must attack the square-cube law directly.
Fractals are geometric structures which have infinite depth of detail, and one of their most intriguing (and mind-twisting) properties is that they can have a non-integer dimension. That is to say, a line is a one-dimensional object, a square a two-dimensional object and a cube a three-dimensional object, but a Koch snowflake is a 1.26-dimensional object, despite looking superficially like an 'ordinary' snowflake at the macro scale. That is to say if you made a steel I-beam with a Koch-snowflake cross section and then doubled its size, you would increase its length by a factor of 2, its cross-sectional area (hence its tensile strength) by a factor of just 1.26, and its volume (hence its weight) by a factor of 2.54 (since the length dimension is not fractal). If you're trying to build a super-light airframe for a plane or zeppelin, such a length-weight ratio is a Big Deal. There are other fractal patterns with even lower dimension, such as the Gosper curve with $D \approx 1.13$, which would make an even better material cross section, or a three-dimensional version of the Koch snowflake with $D=2$ (rather than the normal 3).
What fractal geometries allow you to do is to make things superficially bigger without actually occupying all that extra volume and area. You can keep gravity exactly the same and it will act on 'normal' objects just like it does now, but you can add 'magical' objects and creatures on which normal gravity appears, superficially, to act differently.
Note that for this to work the structure of the object has to be actually fractal, not just the best approximation we can manage with ordinary materials, even down to the atomic scale. If you give up your subdividing when you get down to electrons and quarks, you've missed the point ;-)
