The Heimdallr Underground (帝都地下道) is a passage under the streets of Heimdallr, connecting the Racecourse premises with the Himmel Cemetery.
Trails of Cold Steel III[]
Background[]
Class VII heads to the tunnels under the Racecourse to deal with a monster, but after defeating it, they find Hercules by chance. Class VII defeat the agents, but they use their RAMDAs to escape through a hidden exit. The class gives chase to the agents up to the exit to Himmel Cemetery, but they find that Cedric Reise Arnor and Class I have intercepted them.
With the knowledge that Hercules is using the tunnels, Thors Military Academy' main campus and branch campus begin an operation to capture all 100 Hercules agents, sweeping the underground. However, Class VII is informed that some squads acted strangely and disappeared suddenly. Emma and Celine notice the possibility of them being converted into Noctfamilia, and with Gaius, pinpoints the source of the issue to the Imperial Museum.
During the Summer Festival, Lechter Arundel contacts Rean to ask for help finding the last missing member of Hercules hiding in the underground. After assembling a small army of allies, they head to the underground where they find Cryptids summoned by the residual energy from the previous day and the emotions of the young agent. After rescuing him from the last cryptid and taking him into custody, Lechter reveals his past and his father's actions to Rean and Ash before leaving them to enjoy the rest of the festival.
Maps[]
Enemies[]
- Death Squirm: Chapter 4
- Bloody Fang: Chapter 4
- Murder Organ: Chapter 4
- Blurred Shadow: Chapter 4
- Galactic Shark: Chapter 4
- Magic Knight Heavy Golem: Quest
- Hercules - Rifle: Story
- Hercules - Greatsword: Story
- Mega Kraken: Quest
- Octogeist: Final Chapter
- Tomb Beetle: Final Chapter
- Ultimate Being: Final Chapter
- Deathstench: Final Chapter
- Regenenkopf Type-II: Quest
- Supreme Giant Isopod: Quest
- Dicephalosaurus: Quest
- Great Abyss: Quest
- Magic Knight Azura-Luciel: Quest
Treasure Chests[]
| Key | Contents |
|---|---|
| 1 |  Black Records 1
|
| 2 |  Brave Seed
|
| 3 |  Albion Wolf R
|
| 4 |  Violet Hair - Musse / Power Potion II, Shield Potion II, Mind Potion II
|
| 5 |        All Sepith ×100
|
| 6 |  Passionate Rouge
|
| 7 |  Astral Bell
|
| 8 | Spirit Incense
|
| 9 |  U-Material ×5
|
| 10 | Zeram Powder
|
| 11 |  Hyoushou Gem
|
Quests[]
- Danger Underhoof: Class VII is asked to find and exterminate a monster deep in the underground tunnels.
- Legendary Recipe: A Moon Truffle can be found in the central area of Map 2.
- Heimdallr Tunnels Monster: Mega Kraken can be found in Map 3, in the unexplored side path.
- No Man Left Behind: Lechter asks Rean to find the last Hercules agent in the tunnels.
Fishing[]
| Location | Fish | ||
|---|---|---|---|
 Heimdallr Underground |
Puffer | Hide Shark | Spiky Puffer |
| Cobalt Crab | Blue Marlin | Phantom Shark | |
