Every serious gardener in the world venerates Kew, the British Royal Botanic Gardens in London. And no wonder. Apart from its famous grounds, it houses one of the largest collections -- between 4 and 5 million specimens -- of dried and pressed plants, has a rich and exhaustive botanical library, three museums, a laboratory that carries out extensive plant research and a horticultural school.

But even the window-box gardeners -- a category into which most of the 1 1/4 million annual visitors fall -- know the more popular side of Kew -- the sumptuous gardens, the vast collections of trees and shrubs, the unique buildings. Eight greenhouses are scattered here, on 300 cultivated acres. The earliest was designed by John Nash for Buckingham Palace in 1836; the latest, opened by Princess Diana in July, is a new tropical conservatory named in her honor.

It's such fun -- though not easy -- to get lost here. Broad Walk begins at the main gate, with a blanket of smooth green velvet spreading as far as you can see -- a positive reminder of the incessant English rain. Past the huge cypress and the lilac bed, the macadam curves right to the front of Dutch House, all that remains of Kew Palace. This is a four-story affair with a white, indented, three-arched entry and impressive brickwork in a Flemish bond pattern, with the sides and ends alternating -- fashionable in 17th-century England. Built in 1631 for a merchant of Dutch origin, the house was acquired by George III to help house some of his 15 children, two of whom were married in the drawing room.

Behind the Palace is the Queen's Garden, opened in May 1969. The 17th-century design features a sunken garden, a gazebo and a screen of yew. Only those plants grown 300 years ago are used. A square archway made of hornbeam is trained and clipped: It looks like a hedge on stilts.

The most famous of Kew's buildings is probably the Great Pagoda, near the southeast Lion Gate entrance. Designed in 1761 for Princess Augusta (mother of King George III), the structure is 163 feet high and has 10 deep gray stories, each one with a stylized, rust-colored railing. The building took only six months to complete, which may have something to do with the fact that today it is not open to the public -- for safety reasons.

From the Pagoda site, two long vistas fan out. Cedar Vista angles northwest through the rhododendrons and woodland shrubs toward the lake; the other view is northeast, past the forests of horse chestnuts, maples and Japanese cherries, toward Palm House, a 19th-century tropical greenhouse facing a pond.

Turning left on Broad Walk at the fountain -- past the long, elegant, 18th-century Orangery -- one just glimpses the pitched glass roof of the new Princess of Wales greenhouse. A new stone path gently curves toward the massive glass and steel structure. A maidenhair gingko tree (the label reads 1761) spreads its branches 50 feet, as if to camouflage this latest intruder on its space.

Sunken stone gardens and bold planting lend color and create a foil for the dramatic, diamond-shaped building, which looks something like a glass hill facing south, with the highest point almost 40 feet at the northern end. Giant shadowy forms of tropical curiosities beckon from within.

This is no ordinary greenhouse. The Princess of Wales Conservatory, as it is called, covers about 45,000 square feet and has a straight, sloping roof. (The tall, elegantly curved glass structures popular in Victorian days are pretty but impractical -- rainwater does not readily drain off, and condensation damages plants as it drips. And while the Victorian dome creates a magnificent sky effect, the huge volume of glass increases maintenance problems -- heating, cooling and cleaning.)

A glasshouse should maximize winter light and reduce the build-up of heat in the summer. In the new building, the sloping glass roofs face east and west, so the build-up of heat is significantly cut -- while south-facing vertical glass walls maximize the winter sun. On the outside, the glass is smooth and its iridescence highlights the design. Inside, the glass is textured, screening much of the steel structure, making the building appear lighter and providing a dense backdrop for the spiky cactuses within.

Each of the greenhouse's 10 zones is climatically monitored by a central computer system. An air-pressured atomizer jet system sprays the necessary mist without wetting sightseers. Computerized slats, perforated to admit some light, provide the desired amount of shade, automatically adjusting to weather conditions.

This environmental control allows for 10 different geographic habitats -- from Namib Desert and mangrove swamp through a cloud forest and dry tropics, to imaginative multilevel displays of orchids, ferns, carnivorous plants and begonias. Massive Amazon water lilies (more than six feet across) float in tropical pools surrounded by flowering lilies. Steps lead to the highest vantage point, giving a sweeping vista of bridges, waterfalls and exotic greenery. Steel pillars supporting the roof are encased in cement covered with bog, planted with vines that wind up and around in a most natural way.

To vary the esthetic format within each zone, sandstone from Sussex, limestone from Wiltshire and hardstone from the Lake District were imported. In another area, a rock outcrop with a waterfall is planted with ferns, begonias and other luscious greenery.

About 16,000 herbaceous plants -- some miniature, some grand -- are housed here, enhanced by scrupulous planning and imaginative display. The result is an exciting panorama of exotic, tropical growth.

Kew Gardens (at the Kew Gardens stop on the District Metro line) is open daily -- the gardens from 10 a.m. to sunset, the greenhouses, galleries and museums from 11 a.m. to 5:30 p.m. or sunset, whichever is earlier.

Claire Frankel is a free-lance writer and broadcaster based in London.