a few weeks ago I spent some time trying to recreate a voxel engine such as seen in Minecraft as a technical exercise. It is programmed in Kotlin and I open-sourced it and put it up on github.
https://github.com/jrenner/kotlin-voxel
I thought some might be interested in seeing it so I am posting this here. The project uses libgdx and is gradle based so you can run it simply by cloning the github repo and running:
./gradlew desktop:run
or on Windows:
gradlew.bat desktop:run