To enter the Mermalair, a secret switch must be pressed inside the Shady Shoals rest home, and it will activate a secret door under the couch (much like the entrance to the secret lair of Darkwing Duck which involves a secret door under two recliners). A hole leads down to the lobby of the Mermalair.
There is another entrance, which is a cave like the batcave from the Batman series (most likely for their boat, the Invisible Boatmobile, to get outside). Shady Shoals is located nearby a large cliff which marks the possible location of the cave.
The Mermalair is broken up into the following sections:
The cave entrance of the Mermalair contains the Wall of Superhero Super Gadgetry. This wall contains such gadgets as the Cosmic Ray, the AquaGlove, and the Death Grenade.
An additional tool is the Orb of Confusion. Prolonged exposure to the Orb of Confusion will give its victim confusion. Another tool is the Tickle Belt (as seen in Mermaid Man and Barnacle Boy episode 17).
Another room in this area of the Mermalair is where Man Ray was frozen in tartar sauce.
Additional features include:
Tubes where the I.J.L.S.A member's costumes are contained in.
At the end of the hole at the entrance, the lobby of the Mermalair is the first room. It contains various obstacles to get to the main chamber.
Mermalair main chamber
The Mermalair Main Chamber is found after the lobby. Inside, the Security Computer is present, in which it controls the security system. In addition, funnel machines and the Tower of Power control the power within the Mermalair. Finally, a leisure area, including a Television set, is where Mermaid Man and Barnacle Boy rest.
The Mermalair has a large security system which Mermaid Man and Barnacle Boy use to keep the villains in the villain chamber locked up. In order to shut the whole system down, four buttons must be pressed, along with the main shut-down button, at the main computer.
The Wall of Weapons
The Super Walkie Talkies
The Killer Paddle Ball
The Radio-Powered Satellite Shoe
The Infinity Anchor
The Power Goggles
The Cosmic Ray
The D.I.Y Hammer
The Aqua Glove
"The String"- The Mermalair was presumably destroyed when SpongeBob unraveled all of Bikini Bottom and the Milky Way with the string.