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Is cave exploration an indoor or an outdoor activity?
(infosec.pub)
A "Showerthought" is a simple term used to describe the thoughts that pop into your head while you're doing everyday things like taking a shower, driving, or just daydreaming. A showerthought should offer a unique perspective on an ordinary part of life.
Now that's a good question. I believe it's still outdoors, indoors has the meaning of "comfort from your own home" rather than meaning inside a closed off area. Knitting is an indoor activity, hiking is outdoors
Lots of sports are played indoors that isn't inside someone's home.