Observationally constraining the physical conditions that give rise to massive star clusters has been a long-standing challenge. Now with the ALMA Observatory coming on-line, we can finally begin to probe the birth environments of massive clusters. Our team's Cycle 0 observations of the Antennae Galaxies reveal the molecular clouds in this prototypical starburst in unprecedented detail. Among the exciting findings is the discovery of the first known example of the molecular precursor to a super star cluster. We identified this proto-cluster as a compact CO(3-2) cloud with an exceptionally large line-width. This CO cloud (which our team began colloquially referring to as the "firecracker") has no associated Paβ or thermal radio emission, indicating that star formation has not yet begun -- this allows us to assess the physical conditions before the onset of star formation.