The first thing you notice as you enter Alnwick Garden is all the water. Walk through the new pavilion and visitors' center—an airy, glass-and-wood structure designed by Sir Michael Hopkins—and you'll see a swath of greensward and, beyond it, what looks like a moving hillside. This is the Grand Cascade: 21 weirs, down which tumble 8,700 gallons of water per minute. It's just the first of a series of water sculptures that punctuate the grand, theatrical space, one of the most ambitious horticultural projects in Europe since Versailles. On the grounds of the 12th-century Alnwick Castle in Northumberland, 35 miles from the Scottish border in northeast England, the garden is laid out over 40 acres; when it is finished, sometime in the next three years, it will have cost $73 million.