A guide to some of the world's oddest aquatic destinations, from a massive, deep-blue underwater sinkhole to the world's most dangerous infinity pool

Memorial Day has happened, and the Summer Solstice is nearly here. Meaning, it's basically summer. So get out your swim trunks and head to some unique watering holes with The Atlantic and Atlas Obscura. Featured in this week's edition of "Seven Wonders of the World":

• A massive bright-blue underwater sinkhole
• Three volcanoes surrounding Central America's deepest lake
• A medicinal spa created with the discharge from a geothermal energy plant
• The world's highest and most dangerous infinity pool 
• A reservoir created by a burst dam and the mysterious "American rainmaker"
  
• Two bickering lakes that produce odd weather phenomena 
• A 50-meter-high waterfall with a hidden walkway