Paddington remains the gateway to nearly all the creations of this extraordinary man, who was born in the Hampshire town of Portsea 200 years ago this month. The London terminus is Brunel's best-known work. The vast cathedral of the steam age is the closest reminder we have of the Crystal Palace, which housed the Great Exhibition of 1851. Brunel employed the same technology and construction company as the Palace, creating the imposing three-aisled station roof as a fittingly grand terminus for the Great Western Railway (GWR) from Bristol. The directors of this embryonic line had appointed Brunel as its engineer at the age of 26, entrusting him with the survey and construction of the entire 118-mile railway.
A century and a half on, his structures bear 125mph trains without demur. Critics at the time said that the Maidenhead Bridge across the Thames would collapse. The bridge lies a little to the east of Maidenhead station and was built to stand clear of the masts of Thames barges. It is still the widest and flattest brick arch in Britain, if not the world, and is as graceful today as in 1845 when Turner chose the bridge as the location for his iconic portrait of the new age, Rain, Steam and Speed.
Brunel laid out the line with a gauge of seven feet, almost 50 per cent wider than standard gauge. To see what it looked like, break your journey at Didcot Parkway. Adjacent to it, the Didcot Railway Centre has built a working broad-gauge railway. It will be operating from 29 April-1 May, with a replica Fire Fly locomotive of 1840 and roofless third-class carriage to give visitors a taste of early Victorian travel. The Fire Fly is an early design with wood-sheathed boiler, brass-topped haystack firebox, tall bell-mouthed chimney and original padded leather buffers. A Fire Fly locomotive hauled the first royal train, taking the young Queen Victoria from Slough to London in 1842.
At Didcot, a "transfer shed" illustrates the problems caused at places where broad and standard gauge met; the costs and chaos doomed the minority Brunel gauge, and the last train ran in 1892.
Next stop Swindon, the Wiltshire market town that Brunel and his locomotive superintendent Daniel Gooch chose as the site for the GWR's "principal locomotive establishment". Swindon made trains, carriages and wagons, and dispatched to stations and depots across the network a host of smaller items from soap to treasury tags, fire buckets to brooms.
The works that once employed more than 12,000 people would barely be recognised by Brunel today; some has been demolished, other parts converted to a factory retail outlet, but to see an excellent introduction to the GWR, walk through the foot tunnel under the railway near the station. Located in a former machine shop and blacksmith's shop, the Steam museum displays reconstructed scenes showing how Brunel's railway became woven into society as well as its role as the premier holiday line.
Across the tracks is the railway village that Brunel laid out in 1842, New Swindon. The houses were built with stone excavated from Box Tunnel - which proved the most expensive and troublesome engineering work on the line to Bristol. The tunnel is nearly two miles long, through rock. To bore it, 1,100 men toiled for three years.
Bristol is the city most associated with Brunel. The original line ended in a terminal train shed at Temple Meads station, covered by a false hammerbeam roof based on Westminster Hall in London. When constructed in 1840, it was the largest single-span building in the world. The station, adjacent to the later elegantly curved tracks and platforms in use today, is now partly occupied by the British Empire & Commonwealth Museum. You can walk from Temple Meads beside the River Avon and Floating Harbour to reach perhaps the most extraordinary of Brunel's legacies: the SS Great Britain. In 1970, 127 years after she was launched as the world's biggest ship, she was brought back as a rusting hulk from the Falkland Islands. The transformation into her present state must rank as one of the most outstanding restoration projects ever. Some 322 feet of decking, funnel, masts and skylights have been reinstated, as have most of the deck levels with their cabins and public rooms, fitted out with period furniture. The rooms illustrate the conditions in which the ship took more than 16,000 emigrants to Australia, though she also served as a Crimean troopship.
A special exhibition, The Nine Lives of I K Brunel, is being staged in the adjacent Maritime Heritage Centre until October. Within a whistle blast of the Great Britain is a bridge begun by Brunel when he was 25 but not completed until 1864, five years after his death. Towering above the Severn Gorge, the Clifton Suspension Bridge was completed to a modified design by Brunel's engineering friends as a memorial to him. The chains from Brunel's dismantled Hungerford Bridge across the Thames were incorporated to link the two immense towers.
An even greater structure can be seen about two hours down the track, just beyond Plymouth. Curving around the naval dockyards at Devonport, Cornwall-bound trains slow for the Royal Albert Bridge across the Tamar as though passengers deserve the chance to admire the last of Brunel's works. The Grade I-listed bridge is dominated by the two immense wrought-iron bowed tubes from which the single track railway is suspended.
Brunel was too ill to attend the opening by Prince Albert on 2 May 1859. He saw the completed bridge only once, lying on a couch on a flat truck drawn across by a GWR locomotive. On 15 September that year he died, worn out by a lifetime of achieving the seemingly impossible. He might be amused to know that his terminus at Paddington is still used by millions of Bristol-bound travellers each year - and some continuing on across the Atlantic, though now the Bristol-New York part takes place not aboard a Brunel-designed steamship, but a Boeing.
First Great Western Trains (08457 000 125; www.firstgreatwestern.co.uk) runs half-[hourly services between Paddington, Didcot, Swindon and Bristol.
Didcot Railway Centre (01235 817200; www.didcotrailwaycentre.org.uk), 10am-5pm Sat-Sun and some weekdays, £9.50. Steam (01793 466646; www.steam-museum.org.uk), Swindon, daily 10am-5pm, £5.95. The British Empire & Commonwealth Museum (0117 925 4980; www.empiremuseum.co.uk) daily 10am-5pm, £6.50.
Didcot Railway Centre's Fire Fly steaming weekend is 29 April-1 May, £9.50/£7.50. On 9 September Orient Express's Northern Belle departs from Paddington for a grand reception in Bristol. The fare is £295 (0845 077 2222; www.orient-express.com).