The Giant's Drink was a part of the Mind Game.

It was thought the Giant's Drink could measure how suicidal a student was. In the game, there was a giant who asked the player to drink from one of the two cups in front of him. He said that he would take them to Fairyland.

Normally, one could never get past this part, but Ender Wiggin, instead of choosing between the two poisoned drinks, out thought his enemy and killed the giant by having his character burrow into the giant's eye.

As the giant's corpse fell to the ground, Ender's character found himself in the very same Fairyland that the Giant had promised him.