The world's first Creationist museum - dedicated to the idea that the creation of the world, as told in Genesis, is factually correct - will soon open. Stephen Bates is given a sneak preview and asks: was there really a tyrannosaurus in the Bible?

Just off the interstate, a couple of junctions down from Cincinnati's international airport, over the state line in rural Kentucky, the finishing touches are being put to an impressive-looking building. When it is finished and open to the public next summer, it may, quite possibly, be one of the weirdest museums in the world.

The Creation Museum - motto: "Prepare to Believe!" - will be the first institution in the world whose contents, with the exception of a few turtles swimming in an artificial pond, are entirely fake. It is dedicated to the proposition that the account of the creation of the world in the Book of Genesis is completely correct, and its mission is to convince visitors through a mixture of animatronic models, tableaux and a strangely Disneyfied version of the Bible story.

Its designer, Patrick Marsh, used to work at Universal Studios in Los Angeles and then in Japan before he saw the light, opened his soul to Jesus, and was born anew. "The Bible is the only thing that gives you the full picture," he says. "Other religions don't have that, and, as for scientists, so much of what they believe is pretty fuzzy about life and its origins ... oh, this is a great place to work, I will tell you that."

So this is the Bible story, as truth. Apart from the dinosaurs, that is. As you stand in the museum's lobby - the only part of the building approaching completion - you are surrounded by life-size dinosaur models, some moving and occasionally grunting as they chew the cud.Beside the turtle pool, two animatronic, brown-complexioned children, demurely dressed in Hiawatha-like buckskin, gravely flutter with movement. Behind them lurk two small Tyrannosaurus Rexes. This scene is meant to date from before the Fall of Man and, apparently, dinosaurs.

Theological scholars may have noticed that there are, in fact, no dinosaurs mentioned in the Bible - and here lies the Creationists' first problem. Since there are undoubtedly dinosaur bones and since, according to the Creationists, the world is only 6,000 years old - a calculation devised by the 17th-century Bishop Ussher, counting back through the Bible to the Creation, a formula more or less accepted by the museum - dinosaurs must be shoehorned in somewhere, along with the Babylonians, Egyptians and the other ancient civilisations. As for the Grand Canyon - no problem: that was, of course, created in a few months by Noah's Flood.

But what, I ask wonderingly, about those fossilised remains of early man-like creatures? Marsh knows all about that: "There are no such things. Humans are basically as you see them today. Those skeletons they've found, what's the word? ... they could have been deformed, diseased or something. I've seen people like that running round the streets of New York."

Nothing can dent the designer's zeal as he leads us gingerly through the labyrinth of rooms still under construction, with bits of wood, and the odd dinosaur head occasionally blocking our path. The light of keenness shines from the faces of the workers, too, as they chisel out mountain sides and work out where to put the Tree of Life. They greet us cheerily as we pass.

They, too, know they are doing the Lord's Work, and each has signed a contract saying they believe in the Seven Days of Creation theory. Mornings on this construction site start with prayer meetings. Don't think for a minute that this is some sort of crazy little hole-in-the-corner project. The museum is costing $25m (£13m) and all but $3m has already been raised from private donations. It is strategically placed, too - not in the middle of nowhere, but within six hours' drive of two-thirds of the entire population of the US. And, as we know, up to 50 million of them do believe that the Bible's account of Creation is literally true.

We pass the site where one day an animatronic Adam will squat beside the Tree. With this commitment to authenticity, I find myself asking what they are doing about the fig leaf. Marsh considers this gravely and replies: "He is appropriately positioned, so he can be modest. There will be a lamb or something there next to him. We are very careful about that: some of our donors are scared to death about nudity."

The same will go for the scene where Eve is created out of Adam's rib, apparently, and parents will be warned that little children may be scared by the authenticity of some of the scenes. "Absolutely, because we are in there, being faithful to scripture."

A little licence is allowed, however, where the Bible falls down on the details. The depiction of a wall-sized section of Noah's Ark is based, not on the traditional picture of a flat-decked boat, but one designed by navy engineers with a keel and bows, which might, at least, have floated. "You can surmise," says Marsh. When you get inside, there's nifty computer software telling you how they fitted all the animals in, too.

The museum's research scientist, Dr Jason Lisle, has a PhD in astrophysics from the University of Colorado at Boulder. He realised he was a Christian while he was an undergraduate, but didn't spread it around: "People get very emotional about the issue. I don't believe we should ever be obnoxious about our faith. I just kept quiet." And how did he pass the exams? "I never lied, but if I was asked a question about the age of the universe, I answered from my knowledge of the topic, not my beliefs."

The museum's planetarium is his pride and joy. Lisle writes the commentary. "Amazing! God has a name for each star," it says, and: "The sun's distance from earth did not happen by chance." There is much more in this vein, but not what God thought he was doing when he made Pluto, or why.

Now, we are taken to meet Ken Ham, the museum's director and its inspiration. Ham is an Australian, a former science teacher - though not, he is at pains to say, a scientist - and he has been working on the project for much of the past 20 years since moving to the US. "You'd never find something like this in Australia," he says. "If you want to get the message out, it has to be here."

Reassuringly, on the wall outside his office, are three framed photographs of the former Australian cricket captain Steve Waugh - "cricket's never really caught on over here" - and inside, on his bookshelves, is a wooden model of a platypus. On top of the shelves is an array of fluffy poodle toys, as well as cuddly dinosaurs. "Poodles are degenerate mutants of dogs. I say that in my lectures and people present them to me as gifts."

Ham is a large man with a chin-hugging beard like an Old Testament prophet or an old-fashioned preacher, both of which he is, in a way. He lectures all over the world and spent a month in Britain earlier in the summer spreading the message to the faithful in parish halls from Cornwall to Scotland. "We want to try to convince people using observational science," he says. "It's done very gently but forthrightly. We give both sides, which is more than the Science Museum in London does."

This is true in that the Creation museum does include an animatronic evolutionist archaeologist, sitting beside a creationist, at one point. But there's no space for an animatronic Charles Darwin to fit alongside King David and his harp.

On the shelf behind Ham's desk lie several surprising books, including Richard Dawkins' latest. "I've skipped through it. The thing is, Dawkins does not have infinite knowledge or understanding himself. He's got a position, too, it's just a different one from ours. The Bible makes sense and is overwhelmingly confirmed by observable science. It does not confirm the belief in evolution."

But if you believe in the Bible, why do you need to seek scientific credibility, and why are Creationists so reluctant to put their theories to peer review, I ask?

"I would give the same answer as Dawkins. He believes there is no God and nothing you could say would convince him otherwise. You are dealing with an origins issue. If you don't have the information, you cannot be sure. Nothing contradicts the Bible's account of the origins."

We wander across to the bookshop, which, far from being another biblical epic, is done up like a medieval castle, framed with heraldic shields and filled with images of dragons - dragons, you see, being what dinosaurs became. It is full of books with titles such as Infallible Proofs, The Lie, The Great Dinosaur Mystery Solved and even a DVD entitled Arguments Creationists Should Not Use. As we finish the tour, Ham tells us about the museum's website, AnswersInGenesis.org. They are expecting 300,000 visitors a year. "You've not seen anything yet," he says with a smile.