The Underground is a location from the Mega Man Battle Network series. It is a giant hole in Central Area and is where the Cybeasts were sealed after they rampaged on the Net. There is a Bug Frag Trader Machine located there. The Underground is a two-part area with a giant platform in the second. Whenever a character enters, there is a large roar. Its design is similar to the Undernet's, including its TV noise background, but with purple panels instead of the red ones.
In Mega Man Battle Network 6, the Cybeasts are awakened from the Underground by CircusMan.EXE following his depositing of the collected energy from the participants in the CompuDancing Jamboree. The seal on the area is temporarily removed to facilitate the depositing of the energy and escape of the Cybeasts.
After MegaMan.EXE is taken over by the Cybeast, he retreats to the Underground. He is followed by the Link Navi that Lan Hikari chooses after the area's seal is broken from Mayor Cain's office. However, the Cybeast's presence has caused Evil Spirits to flood the Underground. A NetPolice unit is sent down but defeated. The Link Navi uses the SoulWeapons to defeat the Evil Spirits and makes his way to the giant platform in Underground 2. There, the Link Navi does battle with Beast Out MegaMan and barely wins. CircusMan.EXE arrives and attempts to steal MegaMan but fails. Then Colonel.EXE arrives and fights MegaMan but retreats after losing.
Later, Bass.EXE comes and gains the power of the Cybeasts by absorbing fragments of their data. He revives a copy of Beast Out MegaMan but MegaMan or a Link Navi operated by Lan defeats it. Then Bass attacks Lan's Navi himself but loses. It is the last story-triggered battle against Bass (he can be randomly found in the Graveyard after defeating him here). Also, after the battle, Beast Out MegaMan in his SP form can be found in this area.
- A survey of the area was due to take place on the day of the Preview Gala for the Expo Pavilion. It was presumably cancelled following the invasion of the cyberworld by WWW HeelNavis.