Question

Suppose you have a large boulder in your yard that you’d like to move. How could you break it into smaller pieces without using a sledgehammer?

Answer 1

Is the question that is trying to be answered here how to move the boulder, or how to break up a boulder? If the purpose of the question is how to move the boulder from A to B, then you roll it.

Answer 2

-- Build a long, skinny campfire all around the rock, as close as possible to the rock, so the hot coals are right around the underside of the rock, and the flames lick up and around it.

-- Let it burn there for a few hours, so that a lot of the outside of the rock gets really hot.

-- Throw a big bunch of cold water on top of the rock ... enough so that it runs down the whole outside of the rock.

The thermal stresses that suddenly propagate through the rock, on the surface and for some distance into it, crack a layer of some thickness into several pieces, and the pieces fall off onto the ground.

If the cracking and crumbling doesn't extend far enough in, then just pick up the pieces of the layer that DID crumble off, and then go through the  whole same process again, with the inside smaller rock that remains.