You would be forgiven for thinking researchers had discovered Superman's Fortress of Solitude. The gargantuan gypsum crystals in Mexico's Cave of Crystals measure up to 36 feet (the length of a motor home) and weigh as much as 55 tons (the weight of 11 big elephants). Geologist Juan Manuel Garcia-Ruiz and his colleagues report that for these giants to grow so huge, they must have soaked in mineral-rich waters at a steady temperature of 136 degrees Fahrenheit for hundreds of thousands of years, they write in this month's Geology.