  We theoretically explore the driven-dissipative physics of geometrically
frustrated lattices of cavity resonators with relatively weak nonlinearities,
i.e. a photon-photon interaction smaller than the loss rate. In such systems,
photon modes with zero probability at 'dark' sites are present at the
single-particle level due to interference effects. In particular, we study the
behavior of a cell with three coupled resonators as well as extended Lieb
lattices in 1D and 2D. By considering a partial pumping scheme, with the
driving field not applied to the dark sites, we predict that even in presence
of relatively weak photon-photon interactions the nominally dark sites achieve
a finite photonic population with strong correlations. We show that this is a
consequence of biphoton and multiphoton states that in the absence of
frustration would not be visible in the observables.
