Giants live on solid cloudbanks above the Highlands biome. For unknown reasons (Sorcery? Coincidence? Symbolism?) they look like giant versions of the player looking at them. Although at their size they appear to move slowly, they actually move fairly fast compared to most creatures.
Giants are aggressive towards players they spot, although relative to their size, their sensory range is fairly small. They are difficult to fight with melee weapons, and are better engaged with ranged attacks.