  We present APEX, infrared and radio continuum observations of the
G345.88-1.10 hub filament system which is a newly discovered star-forming cloud
that hosts an unusually bright bipolar infrared nebulosity at its centre. At a
distance of 2.26$^{+0.30}_{-0.21}$ kpc, G345.88-1.10 exhibits a network of
parsec-long converging filaments. At the junction of these filaments lie four
infrared-quiet fragments. The densest fragment (with M=210 M$_{\odot}$,
R$_{\rm{eff}}=0.14$ pc) sits at the centre of a wide (opening angle of $\sim$
90$\pm$15$^{o}$) bipolar nebulosity. $^{12}$CO(2-1) observations show that
these infrared-bright nebulosities are spatially associated with a powerful
molecular outflow from the central fragment. Negligible radio continuum and no
H30$\alpha$ emission is detected towards the cavities, seemingly excluding that
ionising radiation drives the evolution of the cavities. Furthermore, radiative
transfer simulations are unable to reproduce the observed combination of a
low-luminosity ($\lesssim$ 500 L$_{\odot}$) central source and a surrounding
high-luminosity ($\sim 4000$ L$_{\odot}$) mid-infrared-bright bipolar cavity.
This suggests that radiative heating from a central protostar cannot be
responsible for the illumination of the outflow cavities. To our knowledge,
this is the first reported object of this type. The rarity of objects like
G345.88-1.10 is likely related to a very short phase in the massive star and/or
cluster formation process that was so far unidentified. We discuss whether
mechanical energy deposition by one episode or successive episodes of powerful
mass accretion in a collapsing hub might explain the observations. While
promising in some aspects, a fully coherent scenario that explains the presence
of a luminous bipolar cavity centred on an infrared-dark fragment remains
elusive at this point.
