I am currently working on a massive minecraft mod pack and I finally got the most annoying of the underlying work done that made these doable. From top to bottom: floating islands, end surface, mars and finally the nether surface. These are in the early stages of development but just getting them to work at all was super annoying given that modding tools available to me were never designed to do what I want to do with them. Anyway, the terrain you see in the mars screenshot is composed of blocks that were textured based on actual NASA photos of Martian soil and rocks. The white areas are snow "lakes" meant to mimic CO2 and ice deposits on Mars.
All total, the pack adds about 7,000 new blocks and items, over 100 new mobs, surface versions of the nether and end, overworld and nether sky islands, elytra accessible (you can literally fly between them) moon, Venus (based on retro scifi depictions not real life), Mars, Io, Europa, Titan, Enceledus and their associated sky islands in the spaces between, a painting and chiseling mechanic, completely rewritten villager trading system, alloying mechanic, 2 ingredient cooking mechanic (oven), custom biomes and terrain, new redstone mechanics, temporary dimensions (infinitely re-explorable as they never generate the same terrain twice), GUI improvements etc.
