The deeper you go, the hotter it gets and the more dangers you encounter. Go to my discord server, here an invite link: https://discord.gg/vZGP28c
You need to download the modpack in my discord in order to join my server.
Planetcore add many layers underground where you can dig all the way to the core and inside, located below 4800 blocks deep. Each layer are 256 blocks deep and consist of a new rock tier with more valuable ores. You need to find the best ores in each layer and craft a better pickaxe in order to break the next rock tier.
Know more about my mod in curse forge: https://www.curseforge.com/minecraft/mc-mods/planetcore
Goodluck reaching the core!