  Order-disorder transitions between glassy phases are quite common in nature
and yet a comprehensive survey of the microscopic structural changes remains
elusive since the scale of the constituents is tiny and in most cases few of
them take part in the transformation. Vortex matter in type-II superconductors
is a model system where some of the experimental challenges inherent to this
general question can be tackled by adequately choosing the host superconducting
sample. For instance, Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8 + \delta}$ is a type-II
superconductor with weak point disorder that presents a transition between two
glassy phases on increasing the constituents' (vortices) density. At low vortex
densities, the impact of disorder produces the nucleation of a glassy yet
quasi-crystalline phase, the Bragg glass. For high vortex densities the stable
phase, coined as $\textit{vortex glass}$, was proposed to be disordered, but
its structural properties have remained elusive up to now. Here we answer this
question by combining surface and bulk vortex imaging techniques, and show that
the vortex glass is neither a messy nor a hexatic phase: in the plane of
vortices it presents large crystallites with positional correlations growing
algebraically and short-ranged orientational order. However, no dramatic change
in the correlation length along the direction of vortices is observed on
traversing the order-disorder transformation.
