The cave's inside.
The entrance.
The Geeky Junkyard Cave is found in the Desert's Junkyard. It has three trees growing with Robots, Springs, and Gears. It can only be accessed once you reach Star Level 4, since the Junkyard is blocked by a metal gate and you need to incinerate it using the Blowtorch. This area can only be accessed in the Wii/PC versions of MySims.