Lia Fáil is a big rock that sits in Ireland. It is a special rock that has been there for a very long time, maybe even thousands of years. People say that a long time ago, when a king was chosen to rule over the land, he would go to this rock and put his hand on it. Then, the rock would make a special sound that would tell everyone that this person was the chosen king.
That's why it is called the Stone of Destiny. It was like a magical rock that could pick the right person to be king. Now, people go to see this rock because it's an important part of Ireland's history. They can't put their hands on it like the kings did before because it's too precious to touch now. But it's still a really cool rock!