  We present a thorough experimental investigation on single crystals of the
rare-earth based frustrated quantum antiferromagnet Pr$_3$BWO$_9$, a purported
spin-liquid candidate on the breathing kagome lattice. This material possesses
a disordered ground state with an unusual excitation spectrum involving a
coexistence of sharp spin-waves and broad continuum excitations. Nevertheless,
we show through a combination of thermodynamic, magnetometric and spectroscopic
probes with detailed theoretical modeling that it should be understood in a
completely different framework. The crystal field splits the lowest
quasi-doublet states into two singlets moderately coupled through frustrated
superexchange, resulting in a simple effective Hamiltonian of an Ising model in
a transverse magnetic field. While our neutron spectroscopy data do point to
significant correlations within the kagome planes, the dominant interactions
are out-of-plane, forming frustrated triangular spin-tubes through two
competing ferro-antiferromagnetic bonds. The resulting ground state is a simple
quantum paramagnet, but with significant modifications to both thermodynamic
and dynamic properties due to small perturbations to the transverse field Ising
model in the form of hyperfine enhanced nuclear moments and weak structural
disorder.
