The common area is the main and biggest room of the lair, featured in most episodes. It leads to every other room in the lair except for Splinter's bedroom, which can only be accessed through the dōjō. Most of the rooms are accessible with doors, except for the kitchen (which has a cloth room divider) and the dōjō (which has two doorless entrances and some green folding room partitions).
The common area was thoroughly wrecked in The Invasion, Part 1 when the lair was discovered by the Kraang. Kraang Subprime (Irma's true identity) was temporarily defeated here when the spiral staircase fell on top of his unsuited body, apparently crushing him.
- Atomic Robo-X arcade machine
- dōjō's moat
- dōjō's outer ledge
- sitting area (with cushions)
- Space Heroes pinball machine
- spiral staircase (decorative)
- tabletop hockey arcade machine
- tire swing
- training dummy