The 'Horror' channel (on UK Digital Terrestrial TV) occasionally shows episode of The Original Series (but that still doesn't mean that I'm necessarily able to watch them....usually). However, I'm currently watching tv in a hotel (? I think that's what it is, anyway) and such a luxury has allowed me to re-watch:
For the World Is Hollow and I Have Touched the Sky
(which according to Wiki is Series 3 Episode 8....).
I say re-watch: I've not actually seen this episode since the early 1970s and it is just superb in every possible way.
I fully remembered the underpinning trope (oft-used elsewhere in sci-fic, that of ancestral descendants of an extinct race, living on a spaceship that they believe to be a planet, with a cargo-culture misinterpretation of technology and context), but there's so much more to it.
David Alan Mac's observations are spot-on
Unlike D.A.M, I do buy the love affair between Bones and Natira (played by the gorgeous Katherine Greenwood): for me, it works.
If you're a ST fan, especially of The Original Series, what do you think of this interesting and canonical episode? I'm so glad I've had the chance to see it again after half-a-century....