It's a grey, chilly English winter morning and I'm making my way through the busy concourse of Paddington Railway Station. I'm about to begin one of the most eye-opening travel tours of my life. I'm not about to hop on a train out of London; instead, I'm about to hop on one travelling underneath it.

On January 9 th, the London Underground turned 150. This is an important birthday, because the Tube was the first subterranean train system in the world. It was a miraculous feat of Victorian engineering when the first section of the "Metropolitan Railway" opened in Paddington in 1863 - using, incredibly, steam locomotives to travel the tunnels. It was an instant hit, carrying around 26,000 passengers a day.

Like most Londoners, I take the Underground for granted when it works smoothly, whizzing me miles across the city in a matter of minutes, and moan about it when it's overcrowded and delayed. So, in honour of its birthday, I decided it was time to pay homage to this labyrinthine arterial system that lies beneath my feet.

Michelle Buckley, from Insider London, a walking tours company, is my guide. We stand for a few minutes on the concourse, as Buckley explains how the first underground railway journey in history began here, 150 years ago.

"Congestion on London's road is not a modern phenomenon," she says, holding up a copy of a 19th-century engraving by Gustave Dore. This depicts an apocalyptic scene of a London street swarming with horse-drawn carts, omnibuses, pedestrians, traders and flocks of sheep being driven to market. In the 19th century, London's population was booming, growing from one million in 1800 to almost seven million by 1900.

Something needed to be done to get the city moving, and the man who came up with this "outrageous idea" of an underground transport system, Buckley tells me, was the solicitor Charles Pearson. Reactions to his proposals were mixed, with newspapers such as The Times deriding it as an absurd fantasy.

Buckley and I descend into the Tube and travel two stops on the District Line to Notting Hill Gate, an early Tube station that opened in 1868. Buckley points to its beautiful Victorian brick archways, enormous glazed roof and round glass-and-iron pendant lights above us. "They're the original 1868 lights," she says. Baker Street Tube, too, still has these beautiful curved globes hanging over the platforms.

Buckley's talk is a roll call of great entrepreneurial names who made the system happen, but it's the men who cared about the aesthetic experience of travelling on the Tube whom I find most inspiring. There are two characters who stand out in this story: Leslie Green and Frank Pick.

We take the Central line to Oxford Circus, where we emerge on the pavement by Argyll Street. There are two station buildings here, but they are dramatically different in style. One you would scarcely notice. The other, designed by Leslie Green in 1906, is quite different: a distinctive, arched construction covered in rich, oxblood-coloured terracotta tiling. Beautiful Arts and Crafts lettering proudly announces the station's name on the facade, as if it were a West End theatre or grand hotel. There are 27 of Green's stations dotted all over London that share this bold design and exotic, deep red colour. His work began to unify the look of the Tube, making the stations elegant, recognisable landmarks on busy city streets. These were ideas that would be enthusiastically carried forward by the Underground's visionary managing director, Frank Pick, in the 1920s and 1930s.

"Pick cared deeply about the design and look of the Tube; he believed that stations should be places to visit and admire, not just use," explains Buckley.

To see a fine example of station design under Pick's guidance, we travel south to Piccadilly Circus and emerge onto its magnificent circular ticket hallway. This space is pure Hollywood—a glamorous Art Deco design that is as elegant as it is functional and redolent of the Jazz Age, with soft lighting and smooth, pale stone surfaces. It was designed by Charles Holden in 1928, who built several notable Art Deco stations in London's suburbs.

Buckley points out the Deco treasures this station still possesses: orange columns and glass cylinder lights, an original clock, smart lettering on the walls, small, elegant shop booths (still in use) and a magnificent linear world clock encased in a handsome wood and glass case.

Pick not only commissioned great architects and artists (such as Jacob Epstein and Henry Moore) to create beautiful stations and artworks for the Tube, he also introduced its famous bullseye symbol, promoted the use of beautiful artistic poster-advertising that encouraged people to explore their city using the trains and introduced a universal typeface for all of the network's branding.

Londoners have a lot to thank him for. Nikolaus Pevsner, the great British architectural historian, described Pick in 1968 as "the greatest patron of the arts whom this century has so far produced in England, and indeed the ideal patron of our age". Not bad, really, for a railway manager.

In honour of the area's most famous son, Leytonstone Tube station is covered in a remarkable array of mosaics depicting scenes from Alfred Hitchcock films. They include Psycho, North by Northwest and The Birds.

The first, the greatest, the most innovative, the most visionary... the facts, figures and superlatives that I hear during my Tube tour never seem to end. And then there's the simple, ingenious design for which the Tube is most famous: the map, designed by Harry Beck. This iconic design—much copied, never bettered—was first approved and printed in 1933 (thank you, Mr Pick), and was an instant hit. The map isn't geographically accurate, but as any Londoner will tell you, it's how we all mentally imagine our city. If it's not on the map, we can't tell you where it is.

With a life of its own but always intertwined with the city above, the London Underground even has its own species of mosquito, which evolved from an above-ground species that moved to live in the tunnels during excavation in the 1850s.

Even the thick moquette fabric on the Central Line seats tells a story. Buckley makes me closely examine its apparently abstract blue pattern. As I gradually realise, it is a cunningly designed depiction of London's skyline .

It's just another example of incidental beauty that passes unnoticed by most travellers. Stop and look around you, though, and you'll be taken aback by how inspiring the Underground is in its scope, ambition and attention to detail. One rarely thinks of it as a romantic place, but what a lot of love has gone into it over the years. Happy Birthday London Underground.