Blue Temples are the only place you can find a Blue Dragon Egg.
They are made of Blue Bricks in a rectangular shape with a glass roof. The floor is edged with water one block wide inside.
The entrance is in the center of the roof in the form of a slot where water falls down to a hole in the temple floor.
Location[]
Blue Temples are found in Ocean Biomes, on the floor of the ocean.
Dragon Egg[]
The Blue Dragon Egg requires nothing special to get, it sits on top of glowstone inside the temple.