  The breakdown of crystalline order in a disordered background connects to
some of the most challenging problems in condensed matter physics. For a
superconducting vortex lattice, the equilibrium state in the presence of
impurities is predicted to be a "Bragg glass" (BG), where the local crystalline
order is maintained everywhere and yet the global positional order decays
algebraically. Here, using scanning tunnelling spectroscopy (STS) we image the
vortex lattice in a weakly pinned NbSe2 single crystal. We present direct
evidence that the ordered state of the VL is a BG, consisting of a large number
of degenerate metastable states, which is a hallmark of a glassy state. These
results are a significant step towards understanding the disordering of a
lattice under the influence of quenched random disorder with a direct impact on
various fields, including charge density waves, colloidal crystals and
self-organised periodic structures on a substrate.
