  In searching for the neutrinoless double-beta decay of $^{76}$Ge the
GERmanium Detector Array (GERDA) experiment at the INFN Laboratori Nazionali
del Gran Sasso has achieved an unprecedented low background of well below
10$^{-3}$ cts/(keV$\cdot$kg$\cdot$yr) in the region of interest. It has taken
advantage of the first realization of a novel shielding concept based on a
large cryostat filled with a liquid noble gas that is immersed in a water tank.
The germanium detectors are operated without encapsulation in liquid argon.
Argon and water shield the environmental background from the laboratory and the
cryostat construction materials to a negligible level. The same approach has
been adopted in the meantime by various experiments. This paper provides an
overview of the design and operating experience of the 64 m$^3$ liquid argon
cryostat and its associated infrastructure. The discussion includes the
challenging safety issues associated with the operation of a large cryostat in
a water tank.
