The Basement is a room in the Sandersons' House. It's accessible from the foyer via an entrance located directly opposite the front door, and it's where The Sandersons' Giga-Robo is found until it is reactivated.
The room is somewhat small, having brick and tile walls and a stone floor, featuring a set of wooden stair steps leading downward from the entrance. Opposite the entrance is a single outlet. An empty birdcage hangs from the room's ceiling beams and it, alongside some loose bricks within the walls, allows Chibi-Robo to climb up and reach the ceiling beams for easy navigation from above. Captain Plankbeard has sequestered himself here out of pity for the financially poor Sandersons. The Great Peekoe occasionally uses the area as a setting for his dubious business.
Eventually, Chibi-Robo can erect a pair of warp utilibots to quickly ascend and descend the entryway stairs.