Picture by Unknown from DeviantArt
The basic thing that the caves and cliffs update added was more caves and different types of caves.
They added other things like what we all love, Deepslate. Also, they made things like A deep dark.
Also the caves and cliffs update made the world generation more wild and crazy, so be careful not to fall.
Although it doesn't sound too bad the minecraft editors created the deep dark in this update, so be careful when spelunking.
Picture by Unknown from DeviantArt
Picture by Unknown from DeviantArt
some of the types of caves that were added are...
some of the new animals were...