it was called "Lumina Nocturnale" and it was basically a huge underwater city build

which i remember exploring with a mix of awe and fascination and what i think i can identify in hindsight as mild apprehension

as a space that was clearly so lovingly crafted, down to an incredible level of detail, to be a place where a hypothetical super technologically advanced society of people lived their lives

and yet, obviously, by the very nature of the exercise, was completely devoid of people

it's one of my favorite things that i've ever explored in minecraft

but anyways i was inspired to redownload that and explore it again (this time with super cool shaders making everything look incredible)

and since it's a really old map, in the process i had to run it back through an older version of minecraft to convert the map format into something the modern versions can read

and in the process of all this version hopping, some strange things happened

which i did not notice immediately

one of the more relatively recent version updates dramatically extended the overall world height, by way of allowing world generation to extend up to 64 blocks below y=0

and naturally, this map was created before that and could not take advantage of all that space

in fact, in order to fit the whole city in without raising the water above sea level, they had to build it so far down that there was only a one-block-thick layer of bedrock at the bottom separating most of the map from where the void used to be

and at one point while exploring i went into spectator mode and happened to go underneath and glimpse what was underneath it

and there was just. a massive, gaping, irregularly-shaped hole in the world underneath it, leading directly into the void

surrounded by newer chunks with modern cave generation that were probably generated as i loaded in and explored the city

now obviously on paper this sounds fascinating, but given that i was thinking of actually playing on this map a bit, my preference was leaning more toward not having a gaping hellmouth beneath the city

so i tried looking up whether it was possible to re-generate existing chunks in a map, but only below y=0

the results of which were inconclusive and i eventually gave up and instead wound up downloading a map editor and manually filling in the bedrock and deepslate

i could not create actual caves the way natural worldgen would, but i could make a version of the map that would never accidentally drop me into the void (or into a cavernous hole from which i would never escape)

(and, interesting point of order on that note, i did discover in the process that there were gaps in the bottom layer of the build that could have dropped me through the bedrock and into the void if i'd been adventurous enough)

but anyways i hugely underestimated when setting out on this task how long it would take to complete, but the hyperfocus locked me the fuck in, and tl;dr that is how i spent like two hours filling in holes in minecraft instead of sleeping last night

it looks like if i'd taken a more stepwise approach to converting the map through old versions, rather than jumping back to 1.6.4 and then immediately jumping all the way forward to 1.21, the transition to the new world generation might have worked better

so all of that might have been a massive waste of time actually