The London Underground, the iconic transport system that gets busy Londoners from A to B (sometimes via C and D), is celebrating its 150th anniversary in 2013.

The "Tube", the oldest known underground railway in the world, carries more than one billion passengers a year, with around 3.5 million journeys made each day on 11 lines from 270 stations.

To celebrate the Tube's birthday, we want to hear about your most memorable Tube journeys. Use it to commute to work? Attempted the Tube challenge? Documented your first time on the Tube? Witnessed (or been part of) an unexpected marriage proposal? If you are outside of the UK -- do you have an underground system and what is it like?

Send us your stories – and pictures – and you could help shape our coverage on CNN. If you are on Instagram, you can submit images with the hashtags #cnnireport and #tube150.

Please note: London Underground forbids flash photography on its station platforms for driver safety reasons but non-flash photography is fine.