The last pics are of Hierve el Agua. To reach this location, you have to travel a long way on this tiny little mountain road (trust me, it is extremely scary when another vehicle comes from the other direction...and even more frightening when you have to pass a dump truck! They were doing road construction the day I went).
The "lake" is not actually a lake at all. This site has natural springs. The water bubbles out of the ground, making it look like boiling water, hence the name, Hierve el Agua. The water has been trickling out of the ground for centuries, and is what created the white cliffs--the closest thing I can think of is a stalagtite. As the water trickles down, it leaves deposits, making the white formations you can see in the picture.
It's absolutely breathtaking there, and is well worth traversing the tiny, dusty little road for the hour or so it takes to get there. They have dammed up one area, creating the "pool" of water that you can see in the photo. You are even allowed to swim in it if you want to. Although they call them "hot springs", they are anything but! The water was very cold, even though it was still warm outside there.