As a kid in high school I built an FM transmitter including etching the PCB at home and everything. Even thought it was not super high-powered (you're not supposed to build a high-power FM transmitter, especially back then when radio was not digital) it was super fun to be able to speak to this little thing I built and hear it come out from the radio.

As an adult, I built a clone of a Fender Champ guitar amp, completely handwired with an eyelet board like they did back in the day. It sounds amazing for such a simple circuit and is actually an object I enjoy using as opposed to a toy like the FM transmitter was.