Westerlund 1 is a Galactic compact young super star cluster located at a distance of ~5kpc. Following its early discovery (Westerlund 1961) this cluster went largely unstudied until more recent observations revealed a large number of radio sources at its centre (Clark et al. 1998, Dougherty et al. 2010). As a coeval, nearby super-star cluster known to host a significant population of massive evolved stars, Westerlund 1 provides a unique opportunity to study the individual stellar components, how they interact and how they ultimately shape their environment.


We present the results of ALMA (Attacama Large Millimetre/Submillimeter Array) Band 3 observations of Westerlund 1 which reveal in unprecedented detail the population of sources at the core of the cluster at millimetre wavelengths. These include the expansive nebula surrounding the RSG W26 as well as the population of WR stars and cool hypergiants. We will also discuss the exceptionally luminous SgB[e] star, W9 in which the ALMA observations have revealed recombination-line emission that can be used to trace the outflow from the disk-wind in this unusual binary system.