  We demonstrate a new design principle for unidirectionally invisible
non-Hermitian structures that are not only invisible for one specific
wavelength but rather for a broad frequency range. Our idea is based on the
concept of constant-intensity waves, which can propagate even through highly
disordered media without back-scattering or intensity variations. Contrary to
already existing invisibility studies, our new design principle requires
neither a specific symmetry (like $\mathcal{PT}$-symmetry) nor periodicity, and
can thus be applied in a much wider context. This generality combined with
broadband frequency stability allows a pulse to propagate through a disordered
medium as if the medium was entirely uniform.
