Cincinnati Streetcar 1/16/14 Liberty St Thermite Weld (night)

This thermite reaction isn't really any better than any of a dozen other ones you can see on YouTube, but it's in my hometown, and I've seen the weld after the fact. My wife and I happened to be down in that area a few days after this was posted online, and I was able to see the weld shown here. To me, that's pretty cool.

I've been curious for a while how these welds worked - not the chemistry of them, that I understand, but rather how the molten iron was finished into the final weld. So I went hunting an explanation and found this animated video of the weld process.