Where can you walk through all the tropics of the world in an hour or so, experiencing the humidity and temperatures of the South American rain forest, West Africa, and Indonesia? And then slip over to the warm temperate zones of the Mediterranean, South Africa and California?
Oddly enough, in a disused clay quarry in Cornwall, where an extraordinary botanical project that was conceived in the mid 90s and opened in 2001 has already enchanted three million visitors.
The Eden Project is unique, an ongrowing and living experiment partly in the 'open biome' of the Earth itself and partly in two gigantic 'greenhouse biomes' where plants from all over the world are growing as if they were in their natural habitats.
Sitting here in a 'Grecian olive grove' in the Eden Project, with my trusty AlphaSmart 3000 on my lap, I can only register an awestruck appreciation for a project that is truly a mission to help save the planet through education.
Many of the species growing here are in danger of extinction in their own parts of the world. In articles or on TV documentaries they seem distant, a problem 'somewhere else', for 'someone else' to solve. Here, we can see the tiny flowers, or the giant tree trunks, or the funny-shaped fruit, and we can more easily feel for their danger.
But that's the altruistic part. Without doubt, the Eden Project is possibly the best attraction I have visited anywhere in my travels this year.
Sure, it is difficult to match or compare diverse things and places, but there's perhaps a 'satisfaction rating' that can cross such problems. The Eden Project in satisfaction registers at the upper limit.
Maybe a little history is in order, to put Eden into perspective. It came from the germ of an idea by one Tom Smit, who had been in charge of restoring an amazing 'lost garden' at nearby Heligan. That grew in him a fascination of the plant world, and he wondered how best to tell its story.
Like all germs of ideas that become great things, it needed somebody to believe in it. Somebody with money, too. And a place in which to implement it.
Well, the whole idea was to show how important plants are in our world, and to its preservation after a period when mankind has so significantly damaged his environment, perhaps irreparably. So it was fitting that a massive pit outside St Austell in Cornwall, one of the big scars left on the countryside from the excavation of china clay during the last three hundred years, should become the focus of a regenerative project that would also aim to give a new appreciation of the fragile system that keeps us alive.
The idea received £25,000 in feasibility funding from the local council. A leading British architectural practice and two of the country's biggest construction companies worked on the basis that they probably wouldn't get paid. And both of those latter companies - owned respectively by the McAlpine brothers - subsequently even loaned the project substantial funds on the terms that they would only require repayment if the project was a success.
Three years after it officially opened, some £100 million has been spent, acquired from the National Lottery, the European Commission, and Britain's Millenium Commission, as well as from a bank and individual donations.
It was, as the Eden people themselves say, 'a massive risk on a massive dream'. But a dream come true.
The result is, to steal a MasterCard slogan, 'priceless'.
The 'biomes' under cover of special plastic in a metal framework of geodisic construction, are two, and though not by any means the largest element of the project are nevertheless probably the ones which attract most of us. On first view they provide an immediate impression that this is what a colony on Mars might look like.
The Humid Tropics biome is essentially the largest conservatory in the world, has over 1,000 plant species, including the 'canopy' trees that top the world's rain forests and representative examples of those others which live in the gloomier parts beneath.
The temperature ranges between 18degC and 35degC, getting hotter and more humid the higher you climb on the winding paths inside.
Among the exotic plants and their fruits which are familiar to us today are rice, coffee, sugar, bananas and other tropical fruits. Others which never made it to the tables of the developed world, are also here.
The project also provides information of how world trade and our purchasing power relate to the places and the peoples where these are produced.
Fair trade is a key theme, and where exploitation of resources or people is a feature, you'll find the information in Eden. Though not in any finger-wagging way, just a straight presentation of the facts.
There are also presentations on conservation and recycling of some of the products from these plants, as well as the history of how they were developed. Like papyrus, the first form of paper, which was to be the death-knell of clay tablets as much as was the Macintosh computer to hot-metal typesetting.
As against the sticky heat of the first biome, the dry and sunny ambience of the Warm Temperate one is a welcome change (the sun outside was on and off because of the cloud of the day, but when on it felt very mediterranean indeed), and also the brightness of the light compared to the often gloomy parts of the humid zone.
The journeys here are much easier, in climates which most of us around this part of the world are familiar with. Spain, Italy, Greece and the Middle East. To a lesser but growing extent, the Cape Floral Kingdom of South Africa, and, of course, California.
Here again there are lessons incorporated in the displays. Such as how the traditional terraced olive groves in Greece are decaying because young people don't want to work on the land. It is not just the olives that are threatened, but the habitat of more animal species, including insects, reptiles, birds and bats, than are in a typical pine forest.
Having recently been in South Africa for the first time, seeing the amazing varieties of the fynbos plants brought back memories of a memorable short safari. And there were flora from other parts of that country which I hadn't seen. The orange groves of California, on the other hand, were familiar to me, as were scrub deserts that link that state to Mexico. And I have seen at first hand the increasing problems of water supply in that part of the world, which is part of the environmental information given in that part of the exhibit.
The open 'biome', encapsulated in the microclimate of the deep pit in which Eden is built, has an extraordinary variety of colour and species, and it seemed to me that no stray bit of ground is left without something to show us. And distance is no object: from as far away as New Zealand, for example, a particular flax from that country is planted halfway up the side of the pit.
From the time we entered the Visitor Centre, which among other things had a comic but deadly serious interactive display that showed in just a couple of minutes just how much everything we need to live is provided by the plants of this small Earth, we were constantly reminded of the importance of plant life and how we manage and use it will ultimately dictate our mankind's future.
The modern moral tale is: No Plants means no food to eat, no timber to build our houses or make our books, no textiles to make our clothes, no alternative oil when the stocks of what took millions of years of rotting and pressurising of plants to make eventually runs out, and, most fundamentally, no oxygen replenishment so that we can live.
It is a very sobering thought that we human beings are so absolutely dependant on everything else around us. And that, if we don't mind our planet in a very holistic way, what remains of our own species might well have to live in the kind of biomes that are the unique attraction of the Eden Project.
From Eden to Mars on Earth, you might say. We certainly don't want that.