It is located under The Monarch's home in New Jersey and can be accessed through a secret door in the home's library.
- The Morpho Cave features a large Crime Computer which also has a phone that was connected to the mayor's office. It is later revealed that most of the equipment is outdated and unreliable from decades of neglect.
- Storage for the Blue Morpho and Kano's costumes.
- A dock area for the Morpho Scooters.
- A parking spot for the Morphomobile.
- A restroom.
It is not known exactly when the cave was made but it was used by the masked vigilante The Blue Morpho. When the Blue Morpho died, the Morpho Cave fell into disuse for an unknown amount of time.
In Maybe No Go, it was discovered many years later by the contractor Manolo who had been working for the The Monarch to restore his childhood home, stumbled upon the secret passage that lead to the cave. He showed the The Monarch and Henchman 21 how to open the bookcase covered secret passage that lead down to the cave. The Monarch was very shocked that something like the cave was beneath his parent's home.
In Faking Miracles, The Monarch was even more surprised to learn the cave belonged to his father who was a famous super-hero however, he decided to ignore his father's legacy and make use of the cave for his own plans due to it having some of the things he needed after the destruction of his old lair. He also tells 21 of that they are not to inform Dr. Mrs. The Monarch about the cave.
In Rapacity in Blue, the Monarch considers redecorating the cave but changes his mind after watching a video clip of his father on the Crime Computer where he finds out that his father might not have been a good-guy. The Monarch then decides to take up 21's earlier idea of using the costumes of The Blue Morpho and Kano to defeat villains in order to be the only ones left in line to arch Dr. Venture.
During Tanks for Nuthin', Henchman 21 and The Monarch continue to use the cave and still excited from his victory over the villain Haranguetan decided to continue on with his plan of getting rid of the competition but first had to break out the Morphomobile which had been impounded on that same night. The Monarch and 21 considered using the Morpho Scooters but 21 shot down the idea by stating they won't fit in the trunk so they took the bus. The two were successful in freeing the car taking it back to the cave.
In It Happening One Night, Henchman 21 and The Monarch once again use the morpho cave and after finding out The Doom Factory are next in line to arch Dr. Venture they use the Morpho Scooters to head for the villain's base in the city waters.
In A Party for Tarzan, Henchman 21 and The Monarch briefly use the cave and this time 21 takes to using Kano outfit while the monarch goes off to arch his new enemy.
In Red Means Stop, it is revealed that the cave has bathroom which Henchman 21 had been using to hide some of the villains in line for arching Dr. Venture. Throughout most of the episode, two captive villains Maestro Wave and Termite were conversing about their situation until maestro wave decides to kill termite out of hunger. At the end of the episode, Red Death invades the cave with the intent of killing the Blue Morpho for supposedly kidnapping his family but the latter tells him they were never kidnapped and are at his mother-in-law's house. After confirming their location, Red Death reveals that he knows the Blue Morpho is really the Monarch and asks for him to tell the whole reason behinds his recent actions. When the Monarch finishes his story, Red Death relates with him by telling him of his own experience with an old enemy in the past the villain tells monarch to let the other villains do their job and then he'll have his chance. When 21 asks Red Death on how he is so calm over his past actions, the latter asks him the same question which causes 21 to show The Monarch and Red Death the villains trapped in the cave bathroom where he is shocked to find that a majority have killed each other save for one crazed survivor who resorted to eating the bodies. 21 is horrified at the sight as they were never meant to kill each other. Red Death agrees to not tell the GUILD of the monarch's activities provided they let him take care of maestro wave who he presumably kills. While that happens, The Monarch punches 21 in the arm for not telling him of the cave bathroom (as he had earlier searched for one).