Along with being incredibly powerful, Liam Kanno's September 11 memorial made in Second Life (video tour above) is a landmark in immersive design:
"Watching the massive towers fall was unlike anything I've ever seen," Liam continues, explaining his design. "The scale was immense, and I wanted to give as much scale to this build as possible... still, at the same time I had the intention of making it as intimate and private as possible, and wrap the visitor in the space."
Unlike Maya Lin's Vietnam memorial, which this evokes, the names of the fallen remain at a close remove, just out of reach. "Personally for me, when I saw the people fall from the towers... the biggest thing for me is that I could do nothing ot help them... they were there, but no one could catch them. So in the design I have in-world there is about a three foot gap between the names and the walkway."
Read more about it here from my original 2007 post, and the story of how Kanno came to create the memorial: