7.84 avg 14 episodes 8.4 → 7.8 43 min avg
| # | Title | Rating | Votes |
|---|---|---|---|
| 0 | Istanbul | 8.4 | 76 |
| 1 | Scotland's Sin City | 7.7 | 36 |
| 2 | Hitler's Underground Lair | 8.1 | 34 |
| 3 | Rome's Hidden Empire | 7.8 | 29 |
| 4 | Catacombs of Death | 7.6 | 28 |
| 5 | City of Caves | 8.1 | 29 |
| 6 | New York | 7.6 | 33 |
| 7 | London's Lost Cities | 7.5 | 29 |
| 8 | Beneath Vesuvius | 8.1 | 31 |
| 9 | Freemason Underground | 7.0 | 21 |
| 10 | Dracula's Underground | 8.3 | 32 |
| 11 | Secret Pagan Underground | 8.1 | 22 |
| 12 | Underground Bootleggers | 7.6 | 21 |
| 13 | Rome: The Rise | 7.8 | 21 |
7.76 avg 13 episodes 7.3 → 7.3 44 min avg
| # | Title | Rating | Votes |
|---|---|---|---|
| 1 | Underground Apocalypse | 7.3 | 25 |
| 2 | Vietnam | 8.4 | 19 |
| 3 | A-Bomb Underground | 8.7 | 26 |
| 4 | Viking Underground | 7.3 | 29 |
| 5 | Hitler's Last Secret | 7.9 | 22 |
| 6 | Maya Underground | 8.0 | 24 |
| 7 | Mob Underground | 7.3 | 21 |
| 8 | Prophecies from Below | 7.8 | 21 |
| 9 | New York: Secret Societies | 7.5 | 23 |
| 10 | Washington, D.C.: Seat of Power | 7.6 | 25 |
| 11 | Stalin's Secret Lair | 7.2 | 27 |
| 12 | Katrina | 8.6 | 17 |
| 13 | Secret Soviet Bases | 7.3 | 26 |
7.65 avg 13 episodes 7.5 → 7.6 44 min avg
| # | Title | Rating | Votes |
|---|---|---|---|
| 1 | City of Blood | 7.5 | 30 |
| 2 | Okinawa: Tunnels of Hell | 8.1 | 19 |
| 3 | Real Mafia Underground | 7.7 | 24 |
| 4 | Secret Sin City | 6.8 | 27 |
| 5 | Hitler's Trenches | 8.1 | 18 |
| 6 | Barbarian's Lair | 7.6 | 23 |
| 7 | Land of Manson | 7.1 | 20 |
| 8 | Gladiators: Blood Sport | 7.5 | 20 |
| 9 | Secret Holy Land | 7.9 | 19 |
| 10 | Under the Rock | 7.5 | 17 |
| 11 | Tomb of the Lost Mummies | 8.6 | 16 |
| 12 | Gods of War | 7.5 | 18 |
| 13 | Alcatraz Down Under | 7.6 | 18 |
7.09 avg 8 episodes 6.8 → 7.9
| # | Title | Rating | Votes |
|---|---|---|---|
| 1 | Mayan Apocalypse | 6.8 | 18 |
| 2 | America's Military Underground | 6.4 | 15 |
| 3 | America's Unmapped Murder Tunnels | 6.6 | 16 |
| 4 | America's Ancient Ancestors | 6.5 | 18 |
| 5 | The Pirate Queen's Lair | 7.9 | 12 |
| 6 | Templars and the Founding Fathers | 6.9 | 10 |
| 7 | Secrets of the Ancient Metropolis | 7.7 | 8 |
| 8 | The Lost Aztec Colony | 7.9 | 10 |
