"""We headed over to the Maya Riviera on the Yucatan Peninsula, which has a porous topography ripe for underwater sinkholes -- called cenotes,"" explained Barrett.<br />""Each cenote is different -- some are vertical sinkholes, others are caverns or caves.<br />""What makes the cenotes interesting is the mix of fresh and saltwater, which can create these haloclines, which, when the water has been undisturbed by other people, you can literally see."""