I second the vote for the hands of musicians, especially stringed instruments and guitarists. I could watch the left hand of a good guitarist all evening, absolutely entranced (in fact I have done). Not sure if this counts as ‘mundane’ though. People who learn to play the guitar really well are by no means doing something mundane, IMHO.
I love all the details of a byegone age you can see in old movies, especially British films (I’m a Brit) from the 40s, 50s and early 60s. It’s so distinct from today as to practically count as a different universe.
I grew up in the north-west of England in the 60s and 70s, which means I had endless hours to watch and enjoy rain. I still find it fascinating - the sounds, the patterns, the way it completely transforms a landscape (sometimes seemingly immediately), people’s reactions and responses, the sight of rain upon a lake, or raindrops on puddles, the sight of distant rainclouds approaching. And that bright, shiny, glossy world we are temporarily left with afterwards.
I find it fascinating that a large modern supermarket offers several thousand different products. Think of all the people and companies and processes and work that goes on somewhere just so that each one of those product lines can end up on the shelf, and I can just saunter in and help myself to whatever I want, without a moment’s thought.
The heat from the sun is pretty mind-blowing as well. Think of anything you’ve seen on Earth that is really hot - such as a blast furnace or a forest fire or a rocket launch. If you are one mile away from any of those, you won’t feel the heat. Yet we can feel the heat from the sun, and it’s 93 million miles away. Just try to imagine how big and how hot the sun must be.
Skin is amazing. I love the fact that it has all these clever built-in receptors and sensory cells for things like hot, cold, pressure, pain, humidity and so on. Plus it has just the right degree of flexibility. Plus our tactile sense is utterly amazing, and way beyond anything we can reproduce artificially. Plus when you rip or tear it, it just repairs itself!