The Underground, or Tube, system is very extensive as you can see on this London Underground map. There are 11 lines plus the Docklands Light Railway (DLR) and train routes, and using them is pretty easy as long as you know which stop you need! Try to avoid travelling during rush hour (approximately 8am - 9.30pm and 4.30pm - 6pm) unless you feel the need to share the typical London worker's experience of being squashed into Tube carriages with little room to breathe, let alone move.

The Underground operates from about 5am to about 12.30am Mondays to Saturdays; 7am to 11.30pm Sundays although this varies by line and by station. It is therefore best to check at your local Underground Station where they will have a display telling you the first and last trains for that day.

The Underground is, unfortunately, quite an expensive mode of transport, so it is advisable to purchase a Oyster card to make some savings.

If you're travelling in summer, Underground trains tend to get very hot. (Air-conditioning is due to be introduced on some trains in the next few years, but only on the ones that travel - partially - above ground such as the Circle and District lines.) Make sure you carry a bottle of water.

Also note that the Underground network is experiencing a number of well-needed upgrades to its lines and stations. A handful of stations may be closed (for example, Blackfriars Underground station is currently closed until late 2011) but - more likely to affect your journey - is that some Underground lines tend to close during the weekend for engineering works. Different lines are closed on different weekends - it's advisable to take a look at the Transport for London website for details of planned upcoming engineering works. If you can't access the website when you're in London, check for details at your local Underground station. They will usually have posters announcing which lines will be affected that weekend.