Hi. Tardis and I found two large caves underneath three reachable caves. Details about this cave is limited, but it seems to be a vast cave. Tardis said that the cave starts to appear since March. Maybe this cave can access to some special places or reach a void. If you find more information, feel free to post a comment below.
The cave is seen in the bottom left, in the westmost cave in the central grassland
The cave is seen in the bottem right, in the Black Widow cave (grassland)
Special thanks to Tardisfromtornspace for the screenshots in Discord.