When The Beatles first performed at the Cavern on 9 February, 1961, it was so low key it wasn't even advertised.
A year and a half, and 292 performances, later, the group was set for stardom and the Cavern would become one of the world's most famous clubs.
While both Lennon and McCartney had already played the club as The Quarrymen, the un-advertised lunchtime session was George Harrison's first appearance at the Cavern.
The club's lunchtime sessions were popular with young city centre office workers and many would take sandwiches to eat while watching the groups.
The current Cavern has organised a day of events to mark the anniversary and is inviting regulars from the early 1960s to attend. The day of live Beatles music starts with a lunchtime session at 1300 GMT.
A 40-metre long light installation is being created across Mathew Street, called Lucy in the Sky with Diamonds. It will create a ceiling of light along the Cavern Quarter area.
The original Cavern had started life as a jazz venue in 1957 but by 1961 it was moving towards rock and roll - driven more by plain economics than any change in musical taste.
Promoter Sam Leach was instrumental in transforming the Cavern's music policy away from the jazz favoured by owner Ray McFall.
Mr Leach said: "It was a good club and it was exciting.
"Ray McFall hated rock and roll. On March 11th 1961, I did the Iron Door (a rival Liverpool club)  - I did an all night session and it got 1,800 people, that night the Cavern had 50 people in, more musicians than fans.
"Ten days later...Ray gets the message and he turns over to rock and roll at night. Up until then The Beatles only played at lunchtime."
The Beatles had played other Merseyside venues since returning from Hamburg in late 1960, but it was at the Cavern that they would cement their reputation as one of the city's top rock and roll groups.
Many who saw The Beatles at the club claim that was where they were at their best as a live outfit. Mr Leach's first taste of The Beatles was at a venue in Huyton.
He said: "When I first saw them in Hamilton Hall as soon as they started playing, I was just gobsmacked.
"The sound didn't just go over you it went through you.
"John Lennon started with Slow Down and Paul did Hippy Hippy Shake, Stuart did Wooden Heart, Pete Best did Matchbox. The sound was so powerful, it seemed to reverberate around the hall.
"We more or less took American rock and roll and sent it back at them improved. We gave them better sound, which was Merseybeat.
"Make no mistake the Cavern has become the most famous club in the world.
"It makes me smile when they say: 'The Cavern where it all began' - they were the last ones in. But it was an exciting club."
In November 1961, record store manager Brian Epstein saw The Beatles at the Cavern and soon after became their manager.
A record deal with Parlophone would follow but not before the band's sound and image had been subtlety changed.
"The Beatles were the best rock band on the planet", Mr Leach remembers.
"Eppy [Brian Epstein] took them and he groomed them, and took all that rawness out of them, and fair enough it worked. But I know John didn't like it because John was an out and out rock and roller.
"Paul was sensible he knew you had to sort of bend a little bit and become a bit more showbiz. So he went along with Epstein and really, Paul was right."
Paul McCartney returned his roots at the Cavern in December 1999 to play a one-off concert, but it wasn't on the same stage that he had played from almost 300 times in the early 1960s.
The original Cavern club closed in 1973 and was demolished to make way for a ventilation shaft for Liverpool's new underground railway loop line. The shaft was never built and the current Cavern club is recreated across three quarters of the original site, using many of the old club's bricks.
Exactly three year's after their first Cavern appearance on 9 February, 1964, The Beatles performed on The Ed Sullivan Show playing to a record 73 million people across America.
Beatlemania had arrived.
Fifty years ago, a young group stepped on stage in a dark cellar club on Liverpool's Mathew Street for the first of what would be almost 300 appearances.