I was very young, probably as a teenager back in the 90s, when I discovered the existence of Peltier elements for the first time, and that one had been part of

I was very young, probably as a teenager back in the 90s, when I discovered the existence of Peltier elements for the first time, and that one had been part of one of my former CPU coolers for all the time. After an upgrade, I had this now unused CPU fan on my desk, and took it apart for whatever reason (because it and the screwdriver were there, I guess). And there I noticed that as part of the assembly there had been... another thin plate sandwiched between cooler and fan, separate and just held in place with the screws, and I now saw that it also had two wires for power that were spliced into the fan's power cable? Optically, this was clearly just a thin, static slate of something, maybe ceramic. Definitely no moving parts, why in the world does that need power. I curiously applied some voltage, and was amazed that it turned cold! I played around with it a bit, and unwittingly touched the other side of it. Hot, surprisingly hot! It wasn't touching anything, that was just from the air around it! I was mesmerized, good times.