Arthur C. Clark once said "Any sufficiently advanced technology is indistinguishable from magic". What technologies do we have today that would look like magic to people from the past?
I think lasers are pretty wack when you think about them through this lens. A small, wand-like object in your hand can make light appear from seemingly nowhere. If it's powerful enough it can set things on fire or blind people. Not to mention larger ones like laser cutters or the LLD, used to destroy missiles midflight. Thats sure to blow some feudal peasant minds
Speakers still blow my mind. The concept of sound and hearing in general, really. It's incredible how much information, and the variety of information, you can cram into pressure waves. The fact that we have organs and neural pathways that are not only able to, but are solely devoted to the interpretation and transmission of pressure waves built into us is mind boggling. These weird wobbly bones in our head allow us to experience the world and each other. Mind boggling.