Since I last looked into the nature of Westerlund 1, it seems that a whole industry has sprung up to study it.....a search of //adsabs.harvard.edu for recent papers about this object finds plenty of them.
(I have been off studying external galaxies for years....and I have been neglecting the Milky Way e.g. the last three days was devoted to thinking about a particular Abell cluster)
In the optical regime, Westerlund 1 is actually deeply unimpressive , as can be seen in the ESO press release
eso1034 , but it turns out that it is the most massive
young star cluster that we know of in our own Galaxy.
Its total mass of ~100,000 solar masses is well within the range of masses that we find for the (old) globular clusters in our own Galaxy.
Optical image (with the ESO/MPG 2.2m telescope) :
Maybe a CCD with an extended red response might capture it a bit better!
Unfortunately for us, there are 11 (!!) magnitudes of visual extinction in front of this magnificent object.
Because of this, young globular-like star clusters were first discovered in
other galaxies, and only much later in our own Galaxy!
( I seem to recall a study of M83 indicating that it probably has plenty of young star clusters that are of a similar mass to an "old" globular star cluster.)