The London Cycling Campaign is holding 'The Big Ride' later today.
They say it's the largest ever event in support of safer cycling in London, as they call on mayoral candidates to make the streets more inviting for cyclists.
As this promotional video shows, they point to Holland as a blueprint:
They are expecting thousands of Londoners on bicycles, foot, skates and rollerblades.
The event takes place just days before the mayoral election, and will follow a four-mile traffic-free route through central London; from Park Lane to Victoria Embankment.