Here's looking at new

Cambridge conjures up visions of ancient stone, majestic college gateways and monastic courtyards. Yet, popping its head defiantly above the medieval parapets is an exciting different side to this city easily explored in the course of a day on foot or by bicycle. If Modernism and beyond is your thing and you can resist the lure of King's College Chapel, there can be few cities of comparable size with such an array of impressive (if not universally successful) post-war modern architecture. While many of the works of internationally famous designers skilfully weave themselves into the historic fabric of their surroundings, others are daringly designed as iconic stand-alone structures. And with £500m of university building projects on the books, intriguing new edifices are springing up each year. Become an amateur architectural critic for the day and decide on the best of modern Cambridge for yourself.

Cambridge conjures up visions of ancient stone, majestic college gateways and monastic courtyards. Yet, popping its head defiantly above the medieval parapets is an exciting different side to this city easily explored in the course of a day on foot or by bicycle. If Modernism and beyond is your thing and you can resist the lure of King's College Chapel, there can be few cities of comparable size with such an array of impressive (if not universally successful) post-war modern architecture. While many of the works of internationally famous designers skilfully weave themselves into the historic fabric of their surroundings, others are daringly designed as iconic stand-alone structures. And with £500m of university building projects on the books, intriguing new edifices are springing up each year. Become an amateur architectural critic for the day and decide on the best of modern Cambridge for yourself.

Cambridge's wake-up call came after the Second World War when the university had been accused by the architectural historian Nikolaus Pevsner of being stuck in the mud when it came to new building styles. The university's answer was to commission the forward-looking Hugh Casson, architect of the playful Festival of Britain, to design a new Arts campus beyond the Backs, known as the Sidgwick Site. This one-time cricket ground is a good place to begin your exploration of post-war Cambridge.

To reach it from a central starting point at the tourist information office near the market square, head west for Silver Street Bridge and Sidgwick Avenue. At first glance, the Sidgwick Site lives up to its reputation as "an architectural zoo". With its wide variety of buildings by a clutch of this country's leading architects, it represents a display of British post-war Modernism in all its key phases. Original Le Corbusier-like 1960s structures on stilts by Casson have been skilfully added to by the sombre-hued Criminology Faculty (2004) with its geometric façade. However, scuppering the civilised Casson plan for developing the remaining site in a low-key way, James Stirling's lofty History Faculty building, which appeared in 1967, has been labelled, uncharitably, "part bunker, part factory, part greenhouse". This adventure in brick and glass in the shape of an open book has nonetheless survived demolition threats to become a post-war architectural icon. Equally controversial is Sir Norman Foster's glass-fronted Law Faculty Library (1995). According to the architectural historian Gavin Stamp, this giant curving glass structure "... achieves the astonishing feat of making Stirling's History faculty seem diminutive, subtle and even sensible by comparison". Nicknamed by its users "the breadbin", this transparently audacious building is at its most exciting when illuminated after dark.

Tucked behind History is Edward Cullinan's more reticent School of Divinity (2000), its horizontal bands of glass and curving walls echoing a cruise liner. At the northern boundary of the site sits the angular new Faculty of English (2004), its façade softened by pink-hued ceramic tiles. Both Criminology and English were designed by the architects Allies & Morrison, who have taken on the tricky job of rescuing Hugh Casson's much-battered 1950s vision for the Sidgwick Site by reintroducing a more human scale.

Pause next at nearby Newnham College for a miniature delight. Visible from Sidgwick Avenue, the tiny barrel-roofed Rare Book Library (van Heyningen and Hayward, 1982) is a gem of a building which resembles an antique jewel box. Its blue-and-red striped brickwork lends Cambridge's first Post-Modernist building a serious hint of fun.

Head north to the futuristic Centre for Mathematical Sciences (Edward Cullinan, 2001) off Clarkson Road with its cluster of Dalek-like pavilions and grass-covered curving roof. Cullinan's highly original concept likened Cambridge mathematicians to baby swallows and each pavilion is designed as a series of increasingly larger spaces to coax them gingerly out of their "nests" to interact with their fellow boffins. This space-age "ideas factory" is where Professor Stephen Hawking has his roost.

Retrace your steps to the Backs and cross the elegant Garret Hostel footbridge arching over the river Cam. As you pause to watch the punting below, facing you is Trinity Hall's handsome Jerwood Library (Freeland Rees Roberts, 1999) which uses traditional materials such as unseasoned oak to create a spiky modern interpretation of the Elizabethan style. Locals call it "the ship on the Cam". Students beavering away in its cosy book-lined spaces overlooking the river can be distracted by one of the best views in Cambridge.

Carry on up King's Parade towards Trumpington Street and prepare to be bowled over by the university's Judge Institute of Management (John Outram Associates, 1995), a stunning conversion of the former Addenbrooke's Hospital, compete with the original Victorian palazzo-like façade. The Judge's heady confection of detailing and stylistic nod in the direction of ancient Egypt makes it the most colourful modern building in Cambridge. Inside is a lofty pillared atrium with swirling staircases and hanging landings designed to inspire the business leaders of the future to great heights. The public is restricted to the lobby area.

Cross the road to the venerable Fitzwilliam Museum. Wander towards the Old Masters through the sleek new internal courtyard space and light-filled new galleries designed by John Miller (2004). What was once a dreary unused "prison yard" at the heart of the museum has been pressed into service by covering it in a stunning glass roof echoing the British Museum's Great Court. The Fitz's new café is an excellent pit stop for flagging architecture buffs.

Refreshed, take a pre-war detour to seek out one of Cambridge's best Modern Movement buildings, the elegant Mond Building (HC Hughes, 1932) hidden away in the sprawl of the New Museums Site off Free School Lane. The surprise here is the sculptor Eric Gill's external engraving of a crocodile, a visual pun that refers to the nickname given to the sharp-tempered Ernest Rutherford who split the atom at the adjoining Cavendish Laboratory.

Followers and critics alike of the Prince of Wales's conservative tastes should consider walking or biking on to Downing College, off Regent Street, to see the ornate Maitland Robinson Library, designed in 1992 by the Prince's favourite architect, Quinlan Terry. Its impeccable Greek Revival credentials are in perfect harmony with the surrounding early 19th-century's college buildings. Terry, who also built three other buildings at the college, seems to consider Modernism to be the work of the devil.

Back on a more contemporary track, northwards now to Kettle's Yard in Castle Street. Housing a personal collection of great 20th-century art in a carefully conceived informal domestic setting, this is one of Cambridge's real treasures. Check the opening hours to gain access to Sir Leslie Martin's expansive 1970s extension to the trio of once-ruined cottages.

Before your critical faculties give way, you could take in Parkside public swimming pool on Parker's Piece (S&P, 1999), with its rippling wave-like roof, and across the green, what is surely the country's most inventive public loo. Surprisingly, this playful pavilion with chameleon-like external panels that change colour from blushing pink to ice green is by the same architects as the riverside library at Trinity Hall. When it comes to enriching Cambridge's cityscape with innovative architectural forms, regardless of function, Town is clearly determined to keep up with Gown.

This is a sample tour and there are dozens more notable modern buildings to explore. For other self-guided itineraries see Shortcut Guides' A Walk Around Cambridge: Modern Architecture - South, £1.20, available from the tourist information centre, local bookshops or via www.shortcutguides.co.uk. The website www.shape-cambridge.org.uk also offers walks based on contemporary architecture and gives access details. Many buildings can be viewed from the street or other public spaces. Some colleges are happy for you to enter the grounds to view the outside of buildings. Others ask that you report to the porter's lodge on arrival.

Internal access to college or university buildings is seldom allowed. However it can be worth phoning in advance and asking Cambridge Tourist Information, Wheeler Street (0906-586 2526, premium rate applies). For bicycle hire, contact Cambridge Station Cycles (01223 307125; www.stationcycles.co.uk).