A relic of the Old Ones, the power generators under the falls power the monorail which runs far above. The twisted landscape has been through a war worse than any nuclear catastrophe we can imagine, yet the hounds retain their fantastic shape... the beam keeps it's own.
About three hours, a little less. This is very different from how I pictured them when I first read the book, but I like this view of the Hounds.
Here's the final video: [link]