Of course, the rooms were dark, so walking past this always made me feel like I was near the warp core of the Death Star, or something. The lights would be continually in motion; I'm not sure what it was for, but I suspect that each LED mapped to one of the 64,000 CPUs in this beast. Rumor was that it was so fast, it would answer your question before you asked it.
What I hadn't known was that Richard Feynman was the first employee hired at Thinking Machines, Inc. It's quite a story:
That man was so smart that he left smartprints when he walked across the carpet. Figures he had to have been involved with one of the most bad ass computers ever made.
Postscript: it seems that you can go see that very same computer, now on display at the National Cryptologic Museum.