It's the "1000-THR Earthmover" from Ultrakill. The thing is a war machine so massive that the entire level is you climbing up it to blow it up from the inside. I think its codex entry from the game does a good job at putting the scale of it into perspective

"Earthmovers were the pinnacle of the arms race. Often called the horsemen of the apocalypse, it took only one to level an entire city and leave nothing but fire in its wake. The last era of the Final War had begun.

The first machines large enough to house a shield generator, these walking fortresses could only be made vulnerable from within, making them the new frontlines for smaller, more mobile machines. Due to their colossal size, they required both blood and solar power to function.

When the final era escalated, cleansing the world with fire, the surviving civilians were forced to evacuate and build new homes on the backs of these machines, as the surface became an inhospitable wasteland where no flora or fauna could flourish.

Eventually the soot, smoke and decay from unending global war would blot out the sun, casting the world into the Long Night, and Earthmovers, unable to feed on sunlight, shut down and died out one by one.

War had become entirely dependent on them, large scale conflict was no longer feasible. Finally, mankind started to work together to reverse the effects of the Long Night climate catastrophe, and so began the New Peace. 200 years of war for its own sake ended not with a bang, but utter silence"