It wasn't all that long ago that Main Street sidewalks all across Montana -- even in the smallest towns -- would have areas of heavy glass brick embedded in the concrete. They were there for a purpose, allowing light to filter down into the basement "vaults" that extended under the sidewalks in front of many buildings. You don't see them much anymore, and it's kind of too bad.
Here's a shot of some of that glass brick taken from a slightly different angle -- looking up from the basement of an old commercial building. I shot this image up in Havre, back in 2003.