An artist could be forgiven for quaking at the sight of Baltic's level four. You could build an aircraft in this vast space or stage an Olympic gymnastics event.

But Phyllida Barlow (pictured) is not easily ruffled. Exuding calmness and capability, she rose to the challenge by creating a landscape of the imagination using stuff they don't sell in art shops.

Concrete, cheap timber, tarpaulins, bitumen and splattered paint constitute Peninsula, a series of structures which, at the very least, fill the place.

Her late father-in-law would have approved. Mervyn Peake was the artist and writer of the Gormenghast trilogy, the tale of Titus Groan, heir to a huge and crumbling castle.

Phyllida, married to his son Fabian, suggests that Peake's work "is not fantasy. It's actually rooted in quite rigorous observation of the everyday. Those books were written during and just after the war so metaphorically they correspond to that historical period."

Although he suffered a nervous breakdown and was invalided out of the Army in 1942, Peake later visited Belsen concentration camp to do illustrations for a magazine - an experience which he found harrowing. Titus Groan, book one of the trilogy, came out in 1946.

It was due to the war that Phyllida was born in Newcastle in 1944. Her father, Dr Erasmus Barlow, worked in London as part of a wartime unit studying trauma and head injuries but was posted to Tyneside. "The trouble was, by the time wounded soldiers were getting back from the front line, they were usually two or three months into their injuries," explains Phyllida.

"They needed to get to patients sooner than that so they moved the unit up to Newcastle where they could study people who had been injured in the mines."

The Barlows left the North-East in 1947 so Phyllida has no memories of it. But she says her father befriended the philosopher Ludwig Wittgenstein who, in one brief episode of an extraordinary life, was working as a lab assistant at Newcastle's RVI.

"He came to tea every Sunday and ate all the butter and jam, paying no heed to wartime circumstances."

Dr Barlow, now aged 89, attended the opening of Phyllida's Baltic exhibition and went on a tour of Newcastle with some friends.

Phyllida studied at the Slade School of Fine Art in London and is now a professor there, having made her name with a succession of large temporary sculptures made of mundane materials.

She draws a diagram to show how she approached Baltic's level four as a blank canvas, working with paper and pencil to create something which would have a "narrative".

Immediately she decided she wanted to erect a barrier just inside the entrance, hence the towering staithes-like structure made from timber and red tape.

She summarises her art as "my fascination for the world of objects and how I translate the world of objects, which I also think includes human beings. We interact with all these thousands of other objects that are in the world and are often competing with them."

At the back of the gallery, towards the left, is a teetering construction on stilts, while on the right is a dark, painted pile which even the artist calls "a heap of rubbish".

Phyllida says she was very impressed with a teacher who was leading a party of children through the gallery when this particular piece was taking shape.

"She came straight to the heart of the matter, saying to these seven-year-olds, `Now I want to ask you all - is this just a lot of rubbish or is it art?'

"Not one hand went up to say it was a heap of rubbish. I was absolutely flabbergasted. She then went on to ask what they thought the artist needed to make the piece of work. She was really getting those children to think."

Phyllida describes Peninsula as "like a territory to be negotiated". It reminds me of what happens when the tide goes out, leaving barnacled man-made structures high and dry.

She confirms that the outside landscape was a source of inspiration but she didn't set out to recreate anything, not even the "fantastic" High Level Bridge. At best, her creations are "bad copies".

The exhibition runs until April 17.