So big that it happens only once a decade, Floriade is a horticultural exhibition held by the Dutch, who know a thing or two about flowers. With contributions from at least 29 countries, the show opens next month in a new 160-acre park in Haarlemmermeer, nine miles south of Amsterdam. Expect a long valley planted with more than a million bulbs, half covered by a glass canopy the size of four soccer fields (never mind those April showers). A series of 10 islands will hold tree houses and wildlife gardens. For a panoramic view, climb the 130-foot sand-and-grass "hill," inspired by the Pyramid of Cheops. April 6- October 20; 31-23/562-2002; www.floriade.com.