This piece is called Las Meninas by Diego Velázquez. One of the most famous and controversial paintings in the world.
In the center of the painting is the five-year-old princess, Infanta Margarita Teresa. To her left and right are her ladies-in-waiting (meninas) and the rest of her entourage surrounds her. Don José Nieto Velázquez stands in the backlit doorway, ascending or descending the stairs on the back wall.
We can also see two hazy figures staring back at us. This is King Philip IV of Spain and Queen Mariana. To the left of the painting is the artist himself, Diego Velázquez. But what is he painting? The answer to this question is still a mystery more than 350 years later.