  Gravity simulators are laboratory systems where small excitations like sound
or surface waves behave as fields propagating on a curved spacetime geometry.
The analogy between gravity and fluids requires vanishing viscosity, a feature
naturally realised in superfluids like liquid helium or cold atomic clouds.
Such systems have been successful in verifying key predictions of quantum field
theory in curved spacetime. In particular, quantum simulations of rotating
curved spacetimes indicative of astrophysical black holes require the
realisation of an extensive vortex flow in superfluid systems. Here we
demonstrate that despite the inherent instability of multiply quantised
vortices, a stationary giant quantum vortex can be stabilised in superfluid
$^4$He. Its compact core carries thousands of circulation quanta, prevailing
over current limitations in other physical systems such as magnons, atomic
clouds and polaritons. We introduce a minimally invasive way to characterise
the vortex flow by exploiting the interaction of micrometre-scale waves on the
superfluid interface with the background velocity field. Intricate wave-vortex
interactions, including the detection of bound states and distinctive analogue
black hole ringdown signatures, have been observed. These results open new
avenues to explore quantum-to-classical vortex transitions and utilise
superfluid helium as a finite temperature quantum field theory simulator for
rotating curved spacetimes.
