When I finally got around to making myself some thermite, which like all right-thinking people I've been meaning to do since about the age of 10, the thing that surprised me was how bright it is. The combustion temperature of standard aluminium/iron-oxide thermite is about the same as the operating temperature of a light-bulb filament, and that's how bright the whole burning mass shines.
Here's a nice video of the process of thermite welding, which has for more than a hundred years been used to join train tracks together.
There are lots of other thermite welding videos on GooTube, though not all of them let you see the aftermath, when they remove the crucible, knock the mould sectors away and shape the still-glowing weld.
People who do this trick frequently clearly get rather blasé about it after a while, and hang around close to the crucible, or even do stuff like lighting cigarettes off the top of it. I don't think that is actually a very good idea, unless you are absolutely 100% bet-your-eyes-on-it certain that there's nothing on, or even under, the crucible that may unexpectedly flash to vapour when heated to these extreme temperatures.
Classically it's water, or even damp stone, that causes thermite to "explode", but many other substances will too. As I've mentioned before, many metals will boil at thermite temperatures, and there are all sorts of other usually-considered-inert substances that also don't play well with thermite.
Like, for instance, asbestos. The molten iron from a thermite reaction may have cooled enough to not even melt an asbestos mat, but if you put a chunk of asbestos in with the thermite, it will definitely melt and quite possibly boil.
(This ought, at least, to render the asbestos harmless. Asbestos is basically just silica in an unusual shape, so if you melt it and then allow it to cool, you get a lump of non-toxic glass.)