Mbh 14.58.11

"Vaisampayana said, 'When the thunder-armed Indra failed to divert Utanka from his purpose, he united the latter's walking staff with the force of thunder. Then, O Janamejaya, the Earth, opening with those strokes having the force of thunder, yielded a way to the (nether) regions inhabited by the Nagas. By that path Utanka entered the world of Nagas. He saw that that region lay extended thousands of Yojanas on all sides. Indeed, O blessed one, it was equipt with many walls made of pure gold and decked with jewels and gems. There were many fine tanks of water furnished with flights of stair-cases made of pure crystal, and many rivers of clear and transparent water. He saw also many trees with diverse species of birds perching on them. That perpetuator of Bhrigu's race behold the gate of that region which was full five Yojanas high and a hundred Yojanas in width. Beholding the region of the Nagas, Utanka became very cheerless. Indeed, he despaired of getting back the earrings. Then there appeared unto him a black steed with a white tail. His face and eyes were of a coppery hue, O thou of Kuru's race, and he seemed to blaze forth with energy. Addressing Utanka, he said, "Do thou blow into the Apana duct of my body. Thou wilt then, O learned Brahmana, get back thy ear-rings which have been taken away by a descendant of Airavata's race! Do not loathe to do my bidding, O son. Thou didst it often at the retreat of Gautama in former days."