People,
Matali was/is the charioteer of Indra, the King of the celestial realm. In ancient times he was looking for a suitor for his daughter, but counldn't find anyone suitable in the celestial realms, not among the Daityas, Gandharvas, human beings nor among the rishis. So he talked it over with his wife and told her that surely he could find a suitable groom among the Nagas.
So, the Mahabhararta tells that he entered "into the earth". Along the way down, he came across Narada, a celestial sage who wanders across the universe, and always shows up to help out and such things. Narada was on his way down below to see Varuna, the demigod of the waters, and they decided to travel together. Then, this historical narration tells that: "Matali and Narada immersed themselves in the nether regions of the Earth." First, they visited Varuna, then they went to the nether regions beow the Earth and visited the world of the Nagas. "Many species" of Rakshashas were seen by them, and it is described that they visited many huge and opulent cities, such as Hiranyapur.
This is obviously not "the Earth" as we use the name. I think it refers to the worlds below the orbital planes of the solar system.
Cheers!
