A fun experiment I did recently was to measure the speed of sound with my oscilloscope. I wired up a speaker and a microphone at a known distance from each other, connected the oscilloscope to both sides and measured how long it took between sound trigger & reception. I came within several meters/second accuracy which I think is a nice result for a basic home lab setup.

I also track a lot of metrics around the house using Home Assistant. Temperature, humidity, power usage, light levels, heating, but also stuff like total meters of filament used, total objects printed, system metrics. I like statistics and it's fun to compare months/years and clearly see the results of improved isolation for example.