  We study N=2 four-dimensional flux vacua describing intrinsic
non-perturbative systems of 3 and 7 branes in type IIB string theory. The
solutions are described as compactifications of a G(ravity) theory on a Calabi
Yau threefold which consists of a fibration of an auxiliary K3 surface over an
S^2 base. In the spirit of F-theory, the complex structure of the K3 surface
varying over the base codifies the details of the fluxes, the dilaton and the
warp factors in type IIB string theory. We discuss in detail some simple
examples of geometric and non-geometric solutions where the precise
flux/geometry dictionary can be explicitly worked out. In particular, we
describe non-geometric T-fold solutions exhibiting non-trivial T-duality
monodromies exchanging 3- and 7-branes.
