London's $25 billion railway, which took 23 years to build, hits 100 million passenger journeys since opening in May. One station is big enough to fit the city's tallest skyscraper inside.

The Elizabeth line, built by Crossrail, is a highly anticipated railway that opened on May 24. It's the first new underground railway line in the city since 1979.

Since opening eight months ago, more than 100 million journeys have been taken on the Elizabeth Line, Transport for London (TfL) said on Wednesday. About 600,000 journeys are made each day on the railway, making it one of the busiest lines in the UK, it added.

Source: Transport for London

I went for an exclusive tour around two of the central stations on the Elizabeth line in March, as well as a ride on the train. The first station I looked around was at Paddington — one of London's major train stations, which opened in 1854.

Paddington Station on the Elizabeth line is so big that London's tallest skyscraper, the Shard, could fit inside if laid flat, Crossrail CEO Mark Wild said during the tour.

Wild said the Elizabeth line was initially planned 23 years ago, and construction has taken 13 years. After missing several deadlines for its debut, it's finally open.

To mark the launch of the Elizabeth line, Queen Elizabeth II visited the railway, which was named after her. She learned how to add money to an Oyster travel card at London's Paddington station.

For the Queen's funeral on September 19, TfL offered cheaper fares and an extra hour of service on the Elizabeth line. It also created a flower memorial in Paddington station and announced a two-minute silence to passengers.

Source: Insider.

Some stations on the Elizabeth line have artistic details inside. For instance, Paddington Station had clouds printed on the glass ceiling, representing every type of cloud in the sky, TfL Commissioner Andy Byford said on the tour in March.

It cost £1 million, or $1.3 million, per meter to build this tunnel between the Elizabeth line and the Bakerloo line at Paddington Station, Wild said.

Before the tour, there was a glitch in the radio system, which meant the trains had to stop running for two hours. Wild said there were still "niggles and quirks that need ironing out" with the railway.

The tunnels are separated from the platform with glass paneling that slides open when a train arrives. This separates the cooler airflow in the tunnels from the air in the station. The trains are also air-conditioned, unlike most underground trains in London. More than 1,500 kilometers of cable supplies the new line with ventilation, power, and lighting, according to the Crossrail website.

Compared to London Underground tubes and other trains I've been on in the UK, the Elizabeth line trains were bright and spacious. A TfL staffer told me the carriages were 1.5 times bigger than the city's tube trains.

I was able to have a conversation with other people on the train because it wasn't noisy like other underground transport systems. It was also a smooth ride, unlike other journeys I've taken on the tube, which are often bumpy.

I got a good view from the driver's cab of the journey through the tunnels, which are up to 40 meters underground, Wild said.

Eight tunneling machines — each at 1,000 tonnes — were used to created 42km of new rail tunnels below London, according to Crossrail. Twenty-person "tunnel gangs" worked in shifts to create the winding routes between 2012 and 2015, per the company website.

The Elizabeth line serves around 250 million passengers every year, stretching 60 miles east to west across London, per TfL. There are 41 stations along the full route — 10 are newly built and 30 are refurbishments of existing stations.

Elizabeth line trains run from towns east of London, passing through the heart of the city, and towards commuter hubs in the west.

My journey on one section of the railway — from Paddington to Canary Wharf — took around 18 minutes. The same trip using the existing railway network would take around 30 minutes, according to navigation app, Citymapper.

A journey from the financial hub of Canary Wharf to Heathrow Airport takes 38 minutes on the Elizabeth line, at the cost of a normal tube fare. According to Citymapper, the journey normally takes around one hour.

A proposal to create a train running across London from east to west was first aired in 1830, but it has taken almost 200 years to come to fruition.

Construction of the line hit £18.9 billion, that's $25 billion, but Byford said in March that £150 million was still needed to finish the project. Crossrail Ltd was still figuring out how to fund the additional costs, he said.

During construction, nearly 100 million liters of water was pumped out of the station box, enough to fill 40 Olympic-sized swimming pools.

A fragment of woolly mammoth jawbone and a piece of amber estimated to be around 55 million years old were also found and passed onto London's Natural History Museum.

More than 63,000 sleepers and 51,419 meters of rail were installed as part of the line, while around 13,500 meters cubed of concrete was poured in when the tracks were installed. That's enough to fill several Olympic sized swimming pools, according to the Crossrail website.

Parts of the new trains were tested in Vienna under extreme weather conditions, ranging from -25ºC up to +40ºC, according to Crossrail.

Trial runs ended on March 28, Wild said. Ghost runs — journeys without passengers — took place before the line opened in May.

Byford said in March that the Elizabeth line was "late and over budget" but promised "no further slippage."

"Londoners have waited long enough," he said, adding: "This is a game-changer."