Abstract:
The last decade has brought the discovery of a large number of massive (M>10000Msun) young open clusters in the Milky Way, which had previously not been thought to exist. I will present a brief review of these discoveries, emphasizing their use as astrophysical laboratories. I will show the example of the young starburst cluster Westerlund 1, and how it is providing us with a hoard of data on topics such as the binary properties of massive stars, the evolutionary tracks of blue and yellow supergiants or the universality of the IMF. I will also discuss the newly-discovered highly-reddened massive clusters at the base of the Scutum Arm, and our efforts to characterise their population.