Twice as many travellers pass through Oxford Circus every year as pass through all of Heathrow Airport's terminals combined. Yet work to renovate the station's 5.6km of platforms, passageways and corridors will be completed without any closures affecting the 115M passengers.
The work is being carried out under an intense spotlight.
Regular users of the Underground will probably be surprised that Oxford Circus has been picked out early in tube contractor Metronet's seven year, £1.3bn station upgrade programme (see box). Although far from perfect, there are many shabbier stations across the network.
But this is not the point.
Oxford Circus is London Underground's fl agship station.
Three lines - Victoria, Central and Bakerloo - run through it, putting it at the heart of the network. Delivering a much improved facility will be a big statement to those who still question the decision to hand over maintenance and upgrade of the Tube to private contractors.
The work itself, if being carried out on an ordinary site under ordinary site conditions, would be fairly routine.
Platforms and passageways with their tired floors, cracked tiling, flaking paintwork, sub-standard lighting and exposed cabling are being jazzed up with new floors and flash facades with built in lighting; ticket halls are being refurbished with clearer signing;
and a new operations room is replacing the cramped existing facility.
But it is no ordinary site and working time each night is limited - Metronet has a little under four hours, from the time the station closes at 12.40am and London Underground staff claim the station back at 4.30am.
And there are no plans.
Identifying the purpose of the myriad cabling running along passageways and platforms has at times completely foxed survey teams.
'The wiring is a nightmare, ' says designer Duncan Woodburn.
'There are thousands of cables down here and we don't know what they all are. We had to take the roof off the ticket hall and we still can't get our heads around what's up there.' Work can be disrupted at any time - even though the station is closed. Engineering trains carrying out other essential maintenance and upgrades, including Metronet's own work to install moving block signalling on the Victoria Line, must pass through.
Then there are third parties that put up advertising hoardings and maintain vending machines who demand as much as six months notice to move their kit.
And of course there are hazardous materials. Two years of surveys were needed to establish whether asbestos would be a problem. Here, Metronet was lucky: asbestos is only believed to be present in the track switchgear.
'Planning is very important with such a short window of working, ' understates Metronet project manager Ed Maloney.
Preparation for each night's work begins months in advance, he explains.
'Our number one risk is getting all the third parties communicated and moved, ' he says.
The next issue is a logistics one - there is storage space for just three workshifts on site, and lorry deliveries are banned in central London after midnight.
To get around this problem, London Underground closes one station exit early each night, allowing enough time for materials to be offloaded before the delivery deadline.
Work is being carried out in four phases. Phase one, under way now, is the most complicated and includes key rooms such as the operations room and station supervisors room which require approval by the rail inspectorate. It also includes the Central Line platforms and interconnecting passageways.
Phase two then includes the southbound Victoria and Bakerloo line platforms. Phase three tackles the northbound, and phase four the ticket hall and escalators. Construction work will be completed by the end of 2007.