Dana,
I think you have described the magnificence of this object very well, and also its very very very faint showing at the eyepiece.
A remarkably difficult object for visual deep sky observers!
Some of our imagers are reaching magnitude 25, so Westerlund 1 is definitely fair game for them.
Visual observers may have to content themselves with some of the easier-to-see (but less extreme in their properties) Massive & Young star clusters such as:
(1) NGC 3603 (
http://www.iceinspace.com.au/forum/s...light=NGC+3603
)
and
(2) Trumpler 14 (
http://www.iceinspace.com.au/forum/s...light=NGC+3603
http://www.iceinspace.com.au/forum/s...nfrared&page=2 )
and
(3) Messier 11
"What? Messier 11??!?" I hear you all saying, but in fact M11 has about 10,000 solar masses, and looks rather like a
globular star cluster.
("How sad that people ignore the near, and search for the truth afar"
- from
Song of Zazen, by Hakuin)
Oddly, some of the super star clusters in
other galaxies may be easier to see than Westerlund 1, though they will of course be point sources of light at extragalactic distances;
For instance, one of the supermassive star clusters in NGC 1569 is 14.8 visual magnitude, and I believe (at least when I try to rely on my memory) that the single supermassive star cluster within NGC 1705 is also 14.8 visual magnitude.
(The nuclear star cluster in NGC 300 is very prominent in images, but I have to find a magnitude for it)
The most luminous known Super Star Clusters have a luminosity of about visual absolute magnitude 15, which is some four magnitudes brighter than the most luminous 'old' globular star cluster.