From the main docks in Puerto Ayora take a water taxi for less than a dollar to Las Grietas, also known as The Cracks. If you have any questions, ask the guards at the beginning of the docks they can guide you in the right direction.
Once you cross the bay it is a ½ mile to get to the cracks to swim and snorkel, but the walk is half the fun. Signs in every direction are pointing you the right way.
It is a very well maintained back with boardwalks,
beach, and some rough lava rock areas with excellent flora.
Admire the giant opuntias.
There are so many birds to see. Black necked stilts,
white cheeked pintails,
and whimbrels.
One peculiar spot passes by the active pink salt mines.
When you finally get to the crack the color is a stunning deep blue.
Take the steps down and there is a dock to get in, leave your things on the rocks. 
There are three pools to explore. Try to get here as early as possible to avoid crowds, it was very peaceful in the morning. Without even going in you can see colorful fish, we spotted a large eel as well.
The water is chilly, a wetsuit would be appreciated on a cooler day. After swimming take the spur trail up to get a different perspective on the cracks,
and the bay.
You can’t beat this free hiking and swimming adventure in a unique setting in the Galapagos.