The peculiar variable star V838 Mon underwent an extremely unusual outburst in early 2002. Unlike a classical nova, V838 Mon has remained very cool throughout its outburst. It is illuminating the most spectacular light echo in astronomical history, which is being imaged regularly with the Hubble Space Telescope (HST) as well as from the ground. In 2002 and again in 2005, we obtained polarimetric imagery of the light echo, using the Advanced Camera for Surveys onboard HST. These images allow us to determine a purely geometric distance to the star, based upon a method developed by Sparks (1994, ApJ 433, 29). This technique employs the fact that the locus of maximum linear polarization in the light echo should form a ring around the star with a linear radius of cΔt, where Δt is the time since the outburst. We have also serendipitously discovered that V838 Mon belongs to a sparse young open cluster, whose main sequence extends up to spectral type B3 V. Based on photometric and spectroscopic main-sequence fitting, we have determined a distance to the cluster that is completely independent of the polarimetric method. Both the polarimetric and cluster methods yield essentially the same distances, 6.1 and 6.2 kpc. At this large distance, V838 Mon at maximum light was temporarily one of the most luminous stars in the entire Local Group. Its peak luminosity was very similar to that of M31 RV, an event that occurred in the Andromeda Galaxy in 1988. Unlike V838 Mon, however, M31 RV arose from a very old population in the bulge of M31. We will discuss constraints on the outburst mechanisms for these objects based on our findings. Partially supported by STScI grant GO-10618 and by the STScI Director's Discretionary Research Fund.