Underground Go! Go! Go! (地底GO! GO! GO! Chitei Gō! Gō! Gō!) is the 17th episode of Ultraseven.
A cave-in traps Jiro, a miner, 3,000 feet below the Earth's surface. The Ultra Guard is asked to help in learning of the cause of the disruption inside the cave. Referred to as the "Miracle Man", the Ultra Guard learn that Jiro had previously survived a fall from a 700 foot cliff! Moroboshi senses something unusual while in the cave. Upon descending further, Dan learns just who Jiro is -- he's his other self; the human form Ultraseven rescued from the mountain fall before he copied his human form. Using a drilling attack vehicle called the Magma-lizer, the Ultra Guard dig through the rock to find Jiro before the confined area fills up with gas. Trapped beneath the Earth, the Ultra Guard discover an advanced civilization buried inside the rocks below.
- Dan Moroboshi/Jiro Satsuma/Ultraseven (voice) (モロボシ・ダン／ウルトラセブン（声） Moroboshi Dan/Urutorasebun): Kohji Moritsugu (森次 晃嗣 Moritsugu Kōji)
- Anne Yuri (友里アンヌ Yuri Annu): Yuriko Hishimi (ひし美 ゆり子 Hishimi Yuriko)
- Shigeru Furuhashi (フルハシ・シゲル隊員 Furuhashi Shigeru): Sandayū Dokumamushi (毒蝮 三太夫 Dokumamushi Sandayū)
- Kaoru Kiriyama (キリヤマ・カオル Kiriyama Kaoru): Shoji Nakayama (中山昭二 Nakayama Shōji)
- Soga (ソガ Soga): Shinsuke Achiha (阿知波信介 Achiha Shinuske)
- Amagi (アマギ Amagi): Bin Furuya (古谷敏 Furuya Bin)
- Narrator (ナレーター Narētā): Hikaru Urano (浦野光 Urano Hikaru)
- Ultraseven (ウルトラセブン Urutorasebun): Koji Uenishi (上西弘次 Hirotsugu Uenishi)
- Ultraseven Volume 4 Features Episodes 14-17.