Over the years, we've had the pleasure of exploring many parts of the capital that are normally off limits to the public.
We love visiting such places and, judging from our stats, you love reading about them. So we've rounded up 10 of our more unusual adventures into one article. Click through for the full report and pictures.
Into the Northern Outfall Sewer
Like any big city, London is serviced by hundreds of miles of sewers, much of them built in the Victorian era.
We've been lucky enough to experience their foetid charms on two occasions. On our first trip, we found ourselves waist-deep in the Northern Outfall Sewer — the main conduit for north London's filth — where Thames Water explained the difficulties of keeping these antique tunnels in good working order.
Take-home fact: the Greenway linear park near Stratford is actually the roof of the Northern Outfall Sewer. You can follow it all the way from the River Lea to the treatment works at Beckton. Click here for full report and pictures.
Into the River Fleet
Our second sojourn into London's filth took us into the ancient River Fleet, now a medium-sized sewer beneath Farringdon Street.
Take-home fact: you don't really notice the smell — all brain power is diverted to keeping your balance, wading through fast-flowing 'water' in buoyant waders, on a slippery carpet of filth and carrying several kilos of emergency equipment.
Behind the lights of Piccadilly Circus
It's perhaps one of the most photographed sites on Earth, but few ever get to see the lights of Piccadilly Circus from the other side.
A few years back, we clambered up to the giant LCD displays and took some photos of the crowds taking photos of us.
Take-home fact: the signs are never troubled with bird poo — the heat from all that computer power deters avian perchers.
On the tracks of the Underground
Unless you've been evacuated from a train, chances are you'll never get to walk along the tube rails. It's a spooky experience. We took a nocturnal journey along the tracks at Leicester Square station, courtesy of a maintenance crew from Tube Lines (remember them?).
Take-home fact: after the power's been switched off, and no trains are in the tunnel, an eerie whistling noise can be heard. It is the sound of the wind entering the tunnels at far-off Finchley.
Inside a 'haunted' plague pit
When building the London Bridge Experience, at the southern end of said bridge, workers found dozens of human skeletons, thought to be from a plague pit.
A credulous item on BBC News suggested the place was haunted, scaring off the contractors.
We smelt a rat: London's new scary attraction is found to be haunted, just weeks before opening? PR bullshit. Or was it? Click through to find out what happened when we subsequently spent the evening unsupervised with several buckets-full of human remains and lots of booze.
Take-home fact: animatronic zombies look five times more terrifying when they're stacked up next to genuine pieces of human.
Inside the Science Museum's stores
What you see inside the Science Museum represents only 8% of its collection. Much of the rest is housed inside an extravagant Edwardian building near Olympia.
Here, unencumbered by the need for explanatory labels, sit thousands of technological and medical treasures, from Apollo mission patches, to lucky Roman phalluses, to early dentist chairs.
Take-home fact: Blythe House also contains artefacts from the V&A and British Museum. Although they're in the same building and serve similar functions, the triad of institutions have little to do with one another and have separate entrance points.
To the top of Soho's tallest steeple
On Open House weekend 2007, we visited the remarkable church of St Anne's, Soho, whose steeple looks for all the world like a Soyuz space capsule.
At the time, we were able to climb all the way to the top, where we found an ancient ladder, sundry dead birds, an inch of dust and plenty of droppings. Two days later, perhaps by coincidence, perhaps not, we gained the most persistent cough, which lasted all winter. The upper sections of the spire are no longer reachable on Open House weekend, for very good health and safety reasons.
Take-home fact: You can still see the marvellous clock, housed on a lower level of the steeple.
Into the bowels of the British Library
Ever called up a rare book in one of the British Library's reading rooms? If so, your request works its way to your eager paws via a series of Wonka-esque conveyor belts, which lead up from the archive beneath the public parts of the building.
These lower levels also contain a cage full of decrepit computer hardware, awaiting the attentions of digital archivists.
Take-home fact: the Library's basement extends the equivalent of eight storeys deep, with the lower reaches passing close to a tunnel of the Victoria Line.
Into a 'ghost' tube station
Plenty of people have made the decent into Aldwych station, an abandoned tube stop that is now regularly opened up for cultural events by Transport for London.
Not so many, however, have had the privilege of exploring Brompton Road — a Piccadilly Line station that closed in 1934. We were taken down by the Old Underground Company, which is working to rejuvenate and reopen these abandoned stations.
Take-home fact: relics of the Second World War remain in Brompton Road, including a large map plotting London's air defences.
The Clerkenwell Catacombs
If you ever watch a film or TV show featuring endless brick caverns — Sherlock Holmes, say, or Spooks — chances are it was filmed in the tunnels of the Clerkenwell House of Detention.
This prison is long gone, to be replaced by the imposing Hugh Myddelton School, but its catacombs remain. Although the space was once open to the public as a minor tourist attraction, it is now only accessible to film crews and the occasional private event.
Take-home fact: The complex once contained 286 prison cells.
(Note: we always visit places legally, through the proper channels. You can find many more-hardcore, unauthorised explorations of London's hidden bits with a bit of Googling.)
Got any suggestions for other 'secret' places we might explore? Or, better yet, can you grant us access? Leave a comment below, or get in touch with firstname.lastname@example.org