Delidding
Carefully prying off the CPU's metal lid (IHS, the heat spreader) to replace the subpar thermal interface material between the silicon die and the lid — often with liquid metal. It can lower temperatures substantially, but voids the warranty and risks destroying the processor.
Background: under the IHS sits a TIM (thermal interface material) between the die and the lid. When manufacturers use cheap paste instead of solder (Intel for several generations) it becomes a heat bottleneck. Delidding removes the old TIM/glue and replaces it with liquid metal → sometimes 10-20 °C lower. Risk: you can crack the die or components, and liquid metal is electrically conductive (short-circuit hazard). Tools exist to make it safer (delid jigs). A classic extreme-enthusiast hobby. "Direct die" cooling goes a step further and removes the IHS entirely. Related to liquid metal and direct die cooling.