Walnut Wood is a species of wood that grows exclusively in the Safari. Most players tend to not sell the wood because of its low monetary value and aesthetics.
It is roughly the same size as an Elm tree when fully grown, with the exception of this tree's height and branching system. Its exterior is lighter than its interior, but both sport a brown hue.
Its trees can be found at the Safari, which can be easily accessed by paying $100 Money to any of the Bridge Booths to lower the Bridge.
A vehicle is recommended as simply dragging the wood back to the Main Biome is inefficient. A Silver Axe or better is also recommended for efficient chopping. Since the wood is large, a Sawmax 01 or better is recommended for milling purposes.