Tower Subway, London
Firstly props to Kevin Arnold and all credit for cracking this one >> http://www.28dayslater.co.uk/forums/non-public-site-reports-discussions/72964-tower-subway-london-may-2012-a.html
As I understand it this place had been one of the most elusive sites in London for some time, and frankly I felt privileged to have seen it first hand, thanks to Kev

To Quote KA from his thread:
Tower Subway is a bit special
There's a lot of history to this place and whenever underground London is spoken of, the Subway gets a mention
It was the second tunnel to cross the Thames (first one being Brunel tunnel) and since in the first weeks there was a cable pulled train operating in it, the Subway is considered a fore runner of the deep level tube railways
I chanced on another look with GAJ as we had been in the area lifting lids whilst looking for something else, after an uneventful evening and a previous fail here,
was good to actually see something decent before a long journey home..
Constructed in 1869 it was essentially a 1,340 (410 m) long circular tunnel dug beneath the River Thames in central London
It is also notable as the first purpose-built deep railway tunnel in London, designed to take a narrow-gauge cable-hauled railway powered by a static steam engine, so yeah special I'd say
The entrance shafts were fitted with steam-powered lifts for passengers and the tunnel was laid with a 2 ft 6 in (0.76 m) gauge railway
From August 1870 a wooden carriage conveyed a maximum of 12 passengers which were hauled from one side to the other by two 4 horsepower steam engines, one on each bank
The underground railway opened on 2 August 1870, charging 2d for first class and 1d for second class (first class ticket holders having priority when boarding)
Waiting Room
Carriage
However the system was unreliable and uneconomic and closed that December after the company went bankrupt
The car and steam engines were removed, gas lights installed and the passenger lifts replaced with spiral staircases
It re-opened to pedestrians at a toll of 1⁄2d and became a popular way to cross the river, averaging 20,000 people a week (a million a year)
It's main users were described as "the working classes who were formerly entirely dependent on the ferries"
In September 1888 the subway briefly achieved notoriety after a man with a knife was seen in the tunnel at the time when Jack the Ripper was committing murders in nearby Whitechapel
The tunnel closed in 1898, after being sold to the London Hydraulic Power Company, today being used for cities water mains/electrics/fibre optics and of course is well and strictly off limits
Finally, A small round entrance building survives at Tower Hill near the Tower of London's ticket office
This is not the original entrance, but was built in the 1920's by the London Hydraulic Power Company, with a ring of lettering giving the original date of construction and the LHPC
..And here it is present day
(pic 'borrowed' from the interwebZ)
Also the original entrance (seen below) on the south bank of the Thames was demolished in the 1990's to make way for new builds
A much newer concrete shaft has been constructed to facilitate access to the various utilities that run within the tunnel
Below, a concrete extension of approx 150m to where the original southern entrance was once located
It's here presumably the original south shaft would have connected the system (now capped/demolished)
Beyond which, and after a short turn it joins up with the original section of subway
From here on in it's a tight squeeze past the pipes that are now home to the original subway as it passes under the Thames
There is a long low section where water has flooded to around ankle depth which makes traversing through fun
You can also hear faint noises above which sound like the engines from passing boats
Eventually the subway comes to an end as it joins the northern shaft located at the Tower of London
The shaft to the surface kiosk at the Tower of London was much older and far more interesting,
it was however a twat to climb as it was fairly tight and not bag/tripod friendly

Once up, the hatch was also a twat to budge, there was no way we were walking back either
Out we stepped into the night air slamming the age old iron door behind us, now being the only two tourists in sight