Underground world: Seoul's 'super highway' v London's 'rude tube'
3 April 2013 Last updated at 01:52 BST
Getting around big cities can be a frustrating business, but travelling by tube train is usually relatively quick and easy.
The BBC's Underground World series is looking at what it is like to be a commuter around the globe.
Tulip Mazumdar takes a ride on the London tube, which is celebrating its 150th anniversary, while Lucy Williamson hops on the far more recent Seoul underground.