Carry on up the valleys

China, the Himalayas, Camelot: they're not in Wales, but film and TV would have you believing otherwise.

An angry Patrick McGoohan (when wasn't he angry?) being chased by a giant weather balloon while shouting, "I am not a number, I am a free man!" This is an iconic image from cult television series The Prisoner, which celebrates its 35th anniversary next month. The 17 episodes were filmed in the mock Italianate village of Portmeirion (01766 770228; www.portmeirion-village.com) on the coast of Snowdonia in North Wales. It was constructed from 1925 to 1975 as a "home for fallen buildings" by the architect Clough Williams-Ellis, who based his design on the Italian fishing village of Portofino. It has its own restaurants, self-catering cottages, and a luxury hotel overlooking Tremadog Bay. For Prisoner aficionados, a gift shop sells such prime goods as Prisoner jigsaws (£24.95) and Prisoner jackets (£69.99).

Snowdonia National Park has always been a popular site for film-makers and TV producers. Five miles north of Portmeirion, the makers of the Ingrid Bergman film The Inn of the Sixth Happiness (1958) erected a Chinese walled city on farmland at Nantmor, at the foot of the Cwm Bychan valley near Beddgelert. The film was to be shot in China, but a dispute between the film-makers and the Chinese government – over its portrayal of "bound feet" – prompted a hasty rethink. Surprisingly, Nantmor looked authentic, and with the addition of Japanese fighter planes zipping across the sky, the illusion was complete.

Perhaps less effectively, the makers of Doctor Who used the breathtaking Nant Francon Pass, just off the A5 east of Bangor, to double as the Himalayas in the Patrick Troughton story The Abominable Snowmen (1967). Despite Yetis lumbering all over the place, the lack of snow gave the game away. The best vantage point from which to see the spectacular valley is the single- lane track that runs around the west side, beginning at Pont Pen-y-benglog. Be prepared to reverse half a mile if you encounter a car coming in the opposite direction.

Arguably, Snowdonia's most famous appearance was in Carry On Up the Khyber (1968). Here, on the Pass of Llanberis, at the foothills of Mount Snowdon itself, Charles Hawtrey's cowardly Private Widdle was given the task of defending the Khyber Pass from the hideous Burpas. A rustic farm gate, bearing the sign "Please Shut the Gate", added a little veracity.

At the other end of the spectrum, Sean Connery and Richard Gere were the unlikely stars of First Knight (1995), an ill-conceived, £50m take on the legend of King Arthur. A faux Camelot was built next to Trawsfynydd Lake (the immortal cry of "It's only a model!", from Monty Python and the Holy Grail, springs to mind), while other scenes were filmed around the town of Blaenau Ffestiniog. A decade earlier, a disused slate mine at nearby Cwt y Bugail quarry was turned into a secret nuclear plant in the award-winning BBC thriller Edge of Darkness (1985); caverns deep in the mine were once employed for storing the nation's art treasures during the Second World War. The entrance to the plant was filmed miles away, at the Gwynfynydd gold mines in Dolgellau – still a working gold mine (tourist information: www.dolgellau.net, 01341 422888).

For The Englishman Who Went Up a Hill But Came Down a Mountain (1995), film-makers used the unspoilt village of Llanrhaeadr-ym-Mochnant as their main setting, while the mountain of Gyrn Moelfre – a big draw for hang-gliding enthusiasts – featured in the title role.

Moving away from Snowdonia, the Pembrokeshire coastal town of Fishguard (www.fishguard-today.co.uk) became Llareggub ("bugger all" backwards) in the 1971 film of Dylan Thomas's Under Milk Wood. Richard Burton, Elizabeth Taylor and Peter O'Toole spent several weeks in the district of Lower Town, trying to bring the fabled BBC radio play to life (with limited success). Bruce Chatwin's elegiac novel On the Black Hill was brought to life in a 1988 film shot on the Black Hill itself, on the edge of the wonderfully evocative Black Mountains, west of Craswall village. The farm that features in the book was located 20 miles away at Llanfihangel Nant Bran, in the Mynydd Eppynt area.

It's not just the gorgeous Welsh countryside that's featured in films. Cardiff's Allied Steel and Wire Company's Tremorfa Steelworks (once the UK's second largest steel firm, but now an empty shell) was where the final scenes of 1991's A Kiss Before Dying took place. Cardiff docks stood in for Shad Thames in the BBC's 1998 dramatisation of Our Mutual Friend. Swansea was the backdrop for the black comedy Twin Town (1997), with an excursion to a chemical plant at Baglan, Port Talbot, thrown in for good measure.

Finally, that most archetypal of Doctor Who stories, the Jon Pertwee classic The Green Death ("the one with the giant maggots"), was filmed at the Ogilvie Colliery in Deri, along the A469 from Merthyr Tydfil.

The mine workings have now been demolished. But in February 1973 they were witness to glove-operated puppets being attacked by a helicopter dropping lavatory ball cocks.

No less odd was the 1987 Dr Who story Delta and the Bannermen, in which Sylvester McCoy fended off a race of tongue-waggling assassins in a disused holiday camp on Barry Island, off the south coast. Who-de-Who?

Wales Tourist Board, Brunel House, 2 Fitzalan Road, Cardiff, Wales, CF24 0UY (029 2049 9909)