There is a story I've read floating around in my head, which had a few definite elements to it, about a discovery of a highly capable sci-fi-ish subterranean species, who were effectively immortal, by something of the following process;
- they'd scan the brain of the person whom they wanted to "store", and then eject the body into the lava, in a sort-of ritual, or at least with a similar reverence. (Iirc the protag also got offered this, but he declined)
- then they'd grow up a human(?)oid(?) body in a tube, and imprint the memories of that previous brainscan into them by rapidly flashing colors onto their eyeballs, after which they'd step out of the tube themselves. (I also remember one of them commenting something akin to "like shedding a skin" regarding the process)
- Vaguely, I remember this society being carefree and a degree of hedonism, having parties constantly.
- As a last certain point, the protagonist wants to leave, and asks this repeatedly, and they finally grant this request - on one condition that only reveals itself after he is on the surface again; he's brought to the past, and absolutely nobody believes his story.
I remember reading this story at least 6-10 years ago, with a distinct idea that this book is likely from before 2000, at least before the era and idea of smartphones, and with not a lot of influence or "idea" of personal computers.
