Old Rusty is the centerpiece of the playground at Third Street School. It is a large combination jungle gym, slide, and swing set. The place stood for a long time until the Board of Education decided to tear it down. In protest, T.J. Detweiler stood up and inspired others to join in. Peter Prickly decided to confront the students personally, and after unsuccessfully trying to get them off, he resorted to calling their parents, who then recalled their own memories of playing on Old Rusty, and joined the protest as well. Despite the protest being successful, the place collapsed under the weight of the protesters. The construction workers rebuilt the jungle gym anew and T.J. dubbed it "New Rusty".
At one point, Gus Griswald commandeered it to be his home when he thought that his parents were going to move again. Old Rusty had some cloth draped in on the inside to simulate walls, as well as the basic creature comforts. When Gus moves out, Old Rusty goes back to normal.
- Despite the new jungle gym being named "New Rusty", the kids go back to calling it "Old Rusty" later on in the series.
- At Prickly's brother's school, which is like a mirror universe to his own, there is an identical jungle gym named Old Crusty.