The Nature Core is a block added by Random Things. It grows Jungle Leaves and Jungle Wood around it in a 3x3x3 area centered around itself. It can only be harvested with a Diamond Axe or better. (Mining Level Obsidian)
Once placed in a new location, it assembles the structure over a long period of time. It needs to have a clear view of the sky (disregarding the structure) to do this. While it is assembling and after it is finished, nearby surface ground will turn to grass and flowers and tall grass will begin to grow around it. Nearby Saplings and Crops will also grow faster.