If aquarium algae is the last water plant with which you were intimate, the wacky lily pads in Tower Grove Park will be a revelation. Situated in the most absurd, overly civilized corner of the park (nearby points of interest include an antique bandstand surrounded by busts of grumpy classical composers and a manmade pond festooned with phony classical "ruins"), three small but meticulously landscaped lily ponds complete an Arcadian fantasy of the first order. Even if yours is not a lyric sensibility, these bizarre aquatic plantings will torment you with notions of the sublime. Perfectly circular leaves, each with a perfect upturned rim, some of them approaching 5 feet in diameter, float serenely on the pond's surface like a naiad's stepping-stones -- or the Jolly Green Giant's quiche pans. Either way, there's something otherworldly about these magnificent expanses of verdure, and the time to go is now: The lilies are in bloom, and they sport hues of purple and magenta so vibrant you won't believe they're real.