Anyone who's been to Kew will have seen the palm house, the giant water lilies and the pagoda. These are the familiar highlights of the world's favourite botanical garden, created almost 250 years ago on a southwest bank of the Thames. But the 121-hectare site has become so lively and user-friendly that visitors can return again and again and still not exhaust the variety of its landscape and unrivalled plant collections.
Kew is a green universe, inhabited by hundreds of gardeners and researchers, and with its own police force. ("Would you like to tell me exactly how you obtained that wigelia cutting, Madam?") It contains around 10 per cent of the world's flowering plant species, runs all kinds of educational and professional courses, and has recently been declared a world heritage site by Unesco.
But there's also space to enjoy a day out. Although thousands of visitors head there each year, even the so-called "honeypot" areas never get unbearably crowded, while the spreading acres allow lots of scope to get away from it all. Take a picnic (or buy a sandwich), keep walking into the garden's further recesses, then disappear under some magnificent chestnut or cedar tree - you'll feel you're in your own private country park.
But where to start? Most visitors head straight for the glasshouses, to ogle exotic delights such as the Madagascan baobab in the Prince of Wales conservatory, or the fishtail palms in the palm house. But to do things differently, head down towards the Thames, where, this year, a glorious morphine poppy field is in bloom. (Yes, it's legal; the Home Office has given permission.) From there, stroll on through an avenue of small, modern gardens created by this year's horticultural students as part of their studies. "Earth Waves", a sweeping sculpture of raised turf by Heli Markkola, vividly shows how garden design has changed since William Newfield laid out Kew's magnificent vistas back in the 18th century, while "Golden Proportion", by Ellen Sivell, is based on the Fibonacci spiral, a mathematically defined design that governs all kinds of things in nature from the arrangement of sunflower seeds to the whorls of a snail shell.
You will need a good head for heights if you want to tackle the new aerial tree walk, which allows visitors to get up close and personal with the top of a giant redwood, but it's worth the climb. Somehow trees look different when viewed from the top.
Then, if you're a keen gardener, leave plenty of time to wander through the order beds, a systematic display of 3,000 herbaceous plants from 51 families laid out in 126 beds - there are 29 beds for daisies alone. This spilling profusion of flowers, criss-crossed by a rose pergola, is a wonderful summer reminder of the richness and variety of garden plants we all take for granted.
Gail Bromley, education development manager, says this is just about her favourite place in the gardens, "partly because I'm a taxonomist, but also because it's just so pretty".
One of the best things about Kew is that although you're only visiting one place, you're always moving through different landscapes. One moment you're in the rainforest admiring exotic orchards, the next you're in the desert, looking at allotments, or strolling down an avenue of magnificent holm oaks. And it's always changing. "Nothing in nature stays still," says Ms Bromley, "and we're fairly ruthless when we have to be."
New features are planted, old ones are taken up, and there's a constantly changing programme of concerts, exhibitions and drama productions. This summer's festival promotes "New Views of Kew", focusing on features that make you look afresh at the world. There's an exhibition of plant photography in the white peaks exhibition space, and in the marine display in the palm house, a 3-D video allows the astonishing colours and shapes of these smallest of water-borne organisms to wash over you.
But is it a place for children and children's entertainment? Under the current director, Sir Peter Crane, the answer is yes, absolutely. Some years back, when the evolution house, home to the earliest plants - mosses, tree ferns and cycads - was opened, the powers that be turned their noses up at a suggestion to include a model dinosaur, but Sir Peter's first question on walking through it was: "Where's the dinosaur?"
As a result, visitor information is now offered in imaginative, bite-sized chunks - one path-side display shows the prints of a hedgehog, a rabbit and a slow worm captured one night on carbon plates left lying on the grass - and there are plenty of child-friendly features. There's a pond-based wildlife centre, a walk-through badgers' lair, and the brand new climbers and creepers house, where an airy, plant-themed, indoor play park allows under-eights to let off steam while encouraging them to think about the life of plants.
Most big venues that want families to visit now offer something like this, but Kew is a top-class facility with tons of space, a coffee bar viewing area for parents, and exotic diversions such as a cage of palm-sized purple butterflies and a see-through beehive. Then there are the plants themselves. Children will love the steamy palm house. They can marvel at the giant bamboo, which can grow up to one metre a day, or goggle in horror at the deadly strychnos tree, which produces poison that is used in hospitals to paralyse patients' muscles during operations. In the Prince of Wales conservatory they can see the insect-eating Venus fly trap, which apparently knows how to count - it closes when it feels two touches on the hairs inside its leaves.
To save your legs, you can buy a ticket and hop on and off the Kew explorer, an eco-friendly, gas-powered people mover that travels around the garden. And, if it rains, there are plenty of indoor attractions, including a museum showing how plants have been used down the ages.
And whatever you do, don't leave without visiting the spectacular Amazonian water lilies. The Victorians loved them; so do visitors today.
Kew has an extensive education programme and gives detailed teacher guidance on its website. Book a date for the visit, then book a pre-visit planning session and personalised orientation walk with an education officer. Planning packs, Plants Across the Curriculum, are available for key stages 2 and 3 teachers. Short tours on the rainforest and local biodiversity are available. For more information: www.rbgkew.org.uk.
Recorded information, tel: 020 8332 5655; email: firstname.lastname@example.org. School groups, tel: 020 8332 5627.
* The Marianne North gallery: You might easily walk past this, a red-brick construction that looks like the kind of locked-up municipal building you often find in public parks. But push open the door and you'll be astonished. The rooms are lined, edge-to-edge, with more than 800 vibrant paintings of flora and fauna, all by Marianne North, a feisty 19th-century traveller who visited every corner of the world pursuing her painter's passion for plants. She presented her paintings to Kew, built this gallery to house them, then set off on further travels to South Africa, the Seychelles and Chile.
"I love her paintings," says education development manager Gail Bromley.
"She had her own wry, individual way of looking at things. They've often got little things in them that make you laugh."
North was a great character. Born in Hastings in 1830, she travelled alone, painted like fury and wrote lively accounts of her adventures. In Jamaica, she watched locals chase and kill a giant snake that had killed a chicken.
"The butler brought the great body in wound round and round a branch six feet long and as thick as my arm." In India, when flood and fever had laid many low, "everyone was taking opium, so I followed the fashion, prevention being better than cure".
Spend time enjoying her work - in all probability you'll have the place to yourself - then read up on her travels in A Vision of Eden, available at the main shop. When you've finished the book, you will feel as if you've travelled back to the great age of Victorian adventure.
* New Views of Kew, a summer festival, until September 24, including photographic and sculpture exhibitions, and tours. The Royal Society of Arts trail highlights economically important plants around the gardens, and has been created to celebrate the society's 250th anniversary.
Royal Botanic Gardens, Kew, is 10km from central London and takes about 40 minutes on the tube. Take the District Line to Kew Gardens. Mainline trains go from Waterloo. There is free parking in the road outside the gardens.
Opening hours: gardens and glasshouses open at 9.30am. The garden closes at 6.30pm on weekdays, until September 5, and 7.30pm on weekends and bank holidays. See www.rbgkew.org.uk for details. The glasshouses close an hour earlier.
Admission: adults pound;8.50; concs pound;6; children under 16 free if accompanied by an adult.
Anywhere else like it?
* Royal Botanic Garden, Edinburgh, with Britain's tallest palm house, and the world's largest collection of rhododendrons. www.rbge.org.uk.
* National Botanic Garden of Wales, Carmarthen, set in a former 18th-century estate. The first national botanic garden to be created in the UK in more than 200 years. www.gardenofwales.org.uk.
* The University of Oxford Botanic Garden, with 7,000 types of plants in its glasshouses, walled garden, and unusual black borders and autumn borders. www.botanic-garden.ox.ac.uk.
* The Birmingham Botanical Gardens and Glasshouses, with herb and cottage gardens, a fern walk, and the national bonsai collection.
* The Chelsea Physic Garden, a tiny garden in the heart of London, with a pond rockery, and medicinal and grass gardens, plus many holiday workshops for children. www.chelseaphysicgarden.co.uk.
* The Eden Project, standing in a former clay pit in southern Cornwall, and offering warm temperate and humid tropical "biomes" in the world's biggest greenhouses. www.edenproject.com.
Useful curriculum links
Find plants in your postcode via the Natural History Museum's postcode plants database (click on website map, then scroll down to Plants).
www.nhm.ac.uk. Science and plants for schools: www-saps.plantsci.cam.ac.uk.Good links from the Canterbury Environmental Education Centre: www.naturegrid.org.uk.