The Map of Dens is a map of Ninjago that shows the locations of the Serpentine Tombs. It overlays the image of a snake (the Ninjago symbol for "serpent") over Ninjago, with small pictures and a red snake's eye marking each of the tombs along the curves of the snake's body.
The Map of Dens was originally hidden in the icy Hypnobrai Tomb. When Lloyd was imprisoned during Skales and Slithraa's Slither Pit fight, he spotted the rolled-up map poking out of a crack in the ice. After much struggle, Lloyd managed to snatch the map and put it in his pocket before a nearby Hypnobrai Soldier saw him taking it.
When Skales became the new General and banished Lloyd from the tomb, the would-be evil overlord took the map with him. The map briefly led him into the Sea of Sand, where he saw the Ninja boarding the Destiny's Bounty. After glaring at his foes, Lloyd left to find the remaining Serpentine Tombs and left to plot revenge on both the Ninja and the Hypnobrai.
Deciding that the best way to beat a Serpentine tribe was to use another Serpentine tribe, Lloyd used the Map of Dens to seek out the Fangpyre's tomb. After following the map to an eerie graveyard, he found the tomb beneath a gnarled tree and opened it, releasing the Fangpyre and gaining their allegiance.
When the Fangpyre betrayed Lloyd and allied with the Hypnobrai (due to Skales being an old friend of General Fangtom), Lloyd fled to locate another Serpentine tomb. Remembering Skales' mention of the Anacondrai being the most fearsome and powerful tribe, Lloyd followed the Map of Dens back to the Sea of Sand, where he opened the Anacondrai Tomb. Pythor, the last living occupant of the tomb, agrees to become Lloyd's loyal and devoted henchman, while secretly plotting to steal the Map of Dens for himself.
During the Ninja's pursuit of Lloyd and Pythor at Darkley's Boarding School for Bad Boys, the villains end up cornered on the roof. Pythor takes the opportunity to snatch the map from Lloyd, mocking his naivety before turning invisible and making his escape.
Pythor used the map to locate the remaining tombs in his quest to unite the Serpentine and unleash the Great Devourer. Nya eventually caught on to the connection between the location of the dens and the Ninjago symbol for "serpent," allowing the ninja to find the tombs as well—however, they were too late to stop Pythor from awakening the Constrictai and Venomari tribes.
- The Map of Dens was last seen in "Can of Worms," as its purpose was fulfilled. However, the parchment Pythor used to create the map to the Fangblades in "Tick Tock" may have been the back side of the Map of Dens.