It’s even more awesome if you know the story behind it. See, the orchestral score doesn’t actually specify the use of a huge wooden mallet. In fact, it doesn’t specify any particular instrument at all: it just describes a completely hypothetical instrumental sound - “brief and mighty, but dull in resonance and with a non-metallic character (like the fall of an axe)” - and leaves it to the orchestra director to figure out how to actually produce it. Apart from the Big Fucking Mallet, past attempts have included custom-made bass drums, smacking a wooden crate with a sledgehammer, and dropping heavy objects onto the stage from a great height.
I don’t know if Mahler actually intended to troll entire generations of orchestras, but if he did, it totally worked.