Millions of us use it everyday. But photographer Yangchen Lin has captured a side of the Tube most of us probably miss.
A look inside 206 Brompton Road; closed in 1934 and later taken over by the War Office and used as an anti-aircraft operations room.
Peter Smart and Robin Hawkes have made it possible for people to watch every Tube on every line in real-time.
Transport Salaried Staffs Association General secretary Manuel Cortes said it was an example of "gesture politics" by London Mayor Boris Johnson, adding:
"Instead of wasting public money on grandstanding gimmicks, he would be better of focusing on how he caused the dispute in the first place, namely his reckless plan to close all 260 Tube ticket offices.
"Before the walkout, he said he would keep services running with an army of 1,000 volunteers. On the day, the service was at a virtual standstill because only a few hundred actually turned out on the day.
"Now he is using public money on another futile gesture aimed at raising his standing in the Tory party."
The Transport Salaried Staffs Association said the volunteers, who were Transport for London employees, were paid £25 for an eight hour shift plus a further £25 if they worked two shifts over the two-day stoppage over ticket office closures earlier this month.
The union said the total cost would be over £22,000 if it was true that 950 staff volunteered to be on duty during the strike.
The Federation of Small Businesses claims that the recent tube strike cost companies in the capital £600 million in lost working hours, business and productivity.
Members of the FSB lost on average £1,297 during the last tube strike.
– Sue Terpilowski, London Policy Chairman, Federation of Small Businesses
The Capital is one of the most expensive places in the world to do business - all sides of the ongoing dispute need to understand that damaging small businesses in this way leads to a decline in confidence and turnover, and that can mean jobs and capital investment at risk. We urge all sides to find a quick resolution as the average business can ill afford to lose over £2,500 in a two week period.
More than 40 stations are closed this evening. For full details before you travel, visit Transport for London's website.
There is a good service running on the Northern line this afternoon as well as the DLR and the Overground.
The Circle and Waterloo & City lines are closed.
All other lines are running a special service.
Check the TfL website before you travel.
Reports coming in that the route 25 is busier than yesterday in the Stratford area. #tubestrike
There is currently a moderate crowd at Stratford waiting for buses. Buses delayed up to 30mins in the area #tubestrike
Bakeroo - Special service
Circle - Planned closure
Hammersmith & City - Special service
Piccadilly - Special service
Waterloo & City - Planned closure
Central - Special service
District - Special service
Jubilee - Special service
Overground - Part suspended, minor delays
Victoria - Special service
Northern Line - Good service
DLR - Good service