We were so delighted to have seen this, and tried to explain it to several people, but it turns out it's a bit complicated.
So let's try with photos.
Here is what part of the front of the museum usually looks like:
Once we climbed the stairs and got inside the blue box, we marveled at this:
And inside the box on the other side of the museum's entrance was this:
The artist actually built full rooms around the statues, and included them in the interior design...!
I think it would have been absolutely great to be one of the security people on duty in these rooms and watch the visitors. Every single person who I saw coming in (and us included) smiled, laughed aloud or just stood there with their mouth open in awe...
If you want to see how the whole thing was built, the Art Gallery of New South Whales has made a great slide show on flickr here.
And for more crazy installation from Tatzu Nishi, visit his website here (go to projects and click on 'next' to see the locations before and after his interventions).