Port Meadow is so close to Oxford, yet such a contrast to it: a huge expanse of flat, open grassland, full of grazing animals and wild geese, within a stone's throw of the bustling centre of the university town with its cramped pattern of medieval streets.
This makes for a quick escape, and Professor Susan Greenfield takes the opportunity whenever she can. "It's so easy and so nice and you don't need a car," she says. "In just two minutes, you can be somewhere that hasn't ever been under the plough - it's always been common land.
"There's no element of suburbia to go through - quite suddenly, you're there. And what's particularly charming is the animals and the grazing, which is how the grass is kept down, because they don't allow anything mechanical on it. It hasn't changed since medieval times.
"Whenever I go there, I come back feeling re-charged. There's no sign of the 21st century, no pylons, no mechanical instruments of any kind, absolutely nothing. It's just a lovely, gloriously open space, and you feel a sense of serenity and pleasant isolation."
Greenfield, who heads Oxford University's department of pharmacology and is a director of the Royal Institution in London, has just completed a book and a TV series on the human brain, on which she is an internationally-recognised expert.
But if she has a free Saturday to relax, she's likely to choose a full circuit of Port Meadow, first heading north for a three-mile walk along the Thames to Godstow, then crossing the river and coming back down the other side of the meadow along the Oxford Canal.
The first leg starts among rare black poplars, tall and unstable and the subject of a poem by Gerard Manley Hopkins. Then she emerges from the shade to take in the view: "The beauty of it is there's so little between you and the city - there's you, then the river, then just grass and the houses and spires looming up behind."
You can detour to the hamlet of Binsey for a drink in the Perch, or continue past the manicured Godstow Lock and the remains of a convent to reach the Trout, next to a thundering weir. This is where, as an undergraduate, Greenfield had her first drink, choosing lager in preference to Babycham and feeling suddenly grown-up.
From here, you cross the railway for the return leg down the canal. It's closer to houses and people, and reminds Greenfield of Victorian times and the part of Thomas Hardy's novel Jude the Obscure where the hero is dying in his miserable lodgings - "it's the slightly gloomy, industrial part of Oxford - the underbelly".
She prefers walking by herself or with one other person - with more people, she says, it becomes "a dinner party on foot - someone's walking faster or slower than someone else, or you can't all squeeze down a path together, and the whole thing's a mess.
"When you do the kind of thing I do, talking or staring all the time at computers in places with artificial light and air conditioning and so on, it's very good to get back out again among things that are totally natural. I find it an escape, a balm to the soul.
"I'm much more of a sponge when I'm walking, a passive recipient - I switch off, and the positive effect comes later. I feel in control of my life again. I feel on top of things and get a sense of proportion. And of course with strong physical exercise you get the release of endorphins, which give you a sense of well-being.
"The only thing I don't like is walking when it's hot. Spring and autumn are best, and I don't mind getting wet as long as it's not a real soaking. Rain is quite nice because it's quiet, and the smell of the wet vegetation is lovely."
The practicals
Frequent trains and coaches to Oxford from most parts of Britain. National rail enquiries: 0345 484950; for coaches, call National Express Enquiry Line 08705 808080. For general information about Oxford, including accommodation, call the tourist information centre on 01865 726871. OS Landranger map (1 inch to 1 mile) no 164 (Oxford and surrounding area). OS Explorer map (2 inches to 1 mile), no 180 (Oxford, Witney and Woodstock).
· Brain Story, by Susan Greenfield, is published by BBC Worldwide at £17.99. The TV series of the same name is currently showing on BBC2 on Tuesdays at 9pm.
