The Dead Field is a deserted area with dead trees and weeds which may be part of Mutaito's Training Grounds. It can only be accessed by a suspension bridge.
The Dead Field is seen in the Dragon Ball episode, "The Time Room", when Goku goes to the past and trains under Master Mutaito. After Fanfan refused his advances, an infuriated Shen punched her, knocking her out, and kicked Roshi before telling him to bring his "pet" (Goku) and meet him at Dead Field. Roshi hurried to find Goku, and the two rushed to Dead Field, where they found Shen waiting for them. Shen attacked Goku, but it quickly became clear that Goku was the stronger of the two. Shen then revealed Fanfan, still unconscious and tied to a tree, with one of his fellow students holding a knife over her, and threatened to have Fanfan killed if Goku so much as moved.
Despite repeated attacks against his motionless opponent, Shen was still unable to defeat Goku, and finally threw a burning torch down to the ground, igniting the field and trapping Goku and Roshi in a circle of flames. Using a technique he had learned from Mutaito, Goku managed to open a path in the flames so that he and Roshi could escape. Fanfan had meanwhile regained consciousness and incapacitated one of her captors with a kick. Another of Shen's friends was about to hit Fanfan, but was stopped by Mutaito, who had just arrived on the scene.
One of the grounds at Mutaito's Training Grounds in Dragon Ball Z: Attack of the Saiyans looks similar to the Dead Field. It is likely this area, as it can only be accessed via a suspension bridge, which is apparently meant to be the bridge seen in the anime (or one like it).