Underground
Subterranean
noun, の adjective
If you're in the middle of the ground, then you're most likely underground. Are you a moleperson? That's pretty cool.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
地中には、たくさんの虫がいます。
There are many insects underground.
地中にはレーダーがある。
There is a radar underground.
お父さん、地中の生活はどうですか？
Dad, how's your life underground?