Building:Trinity House is the UK's General Lighthouse Authority, and has been based in a Georgian building overlooking Tower Hill since 1796. The interior was gutted by an incendiary bomb in 1940, then painstakingly recreated using photographs from a spread in Country Life. [take a tour] A look around: It all looks lovely today, with history reverberating from every surface, as befits an organisation with deep naval pockets. A huge collective portrait dominates the loftylobby at the top of the main stone stairs, beyond which are rooms with even more impressive painted ceilings and maritime memorabilia. The postwar extension is rather more functional, featuring stained glass removed from Mile End and windows commemorating royal patronage, plus plenty of space for hosting receptions or ceremonial. I'm guessing nowhere else in London boasts a huge silver lighthouse, on silver rocks, locked securely in a silverware case.
Building: Not to be confused with the Newham suburb, this lengthy building faces the Thames waterfront between London Bridge and the Tower, and is where ships' captains would have come to pay duties on their cargoes. The current building is about 200 years old, its warehouse interior mostly modified into austere government offices, but the Long Room where the counters for payment used to be survives intact. A look around: Custom House is still used by Her Majesty's Revenue and Customs, so when you visit for Open House what you're really coming to is an HMRC Roadshow. Chirpy geezers will explain how they spot cigarettes being smuggled through airports, how they crack down on under the counter laundering and how they fly abroad to nail tax-avoiding fraudsters. Trained dogs will practise suitcase sniffing in the courtyard. And when eventually you reach the Long Room prepare to doubletake when you see rows of drab government desks squished in beneath a historic ceiling. My thanks to the dozens of civil servants who turned out at the weekend to smile and nudge us round, in what to them is simply their daily place of work.
Building: Not Lloyd's of London, but from the same coffeehouse roots, Lloyd's Register was founded in 1760 to serve the needs of merchant shipping. Their Renaissance-style HQ in Fenchurch Street dates from the turn of the 20th century, and is the very building used by Monty Python in their swasbuckling skit The Crimson Permanent Assurance. A century later Richard Rogers added a twin-towered steel and glass extension, bolted onto the side behind a churchyard garden. A look around: They've got the Open House experience nailed here - first a chat from someone knowledgeable in the glazed atrium, then directed off round a self guided trail so the next batch queueing in the churchyard can troop in. Follow the arrows to meet an archive conservator and peruse a model oil rig, then move on into the serious palazzo with its OTT decoration. The Old Library boasts barrel-vaulting and bookcases with rosewood inlay, but the main event is the General Committee Room up the marble staircase. An Italianate saloon embellished with nautical symbolism, beneath a painted ceiling echoing the Sistine Chapel, this dizzying space is proof that trade pays.
Building: You've likely seen the building at the head of the approach to the Millennium Bridge, a plain glass box on the corner of Queen Victoria Street. The Sally Army's nerve centre is the result of downsizing in 2004, with the majority of the site rented out to a hotel to help pay for the missionary upgrade. The architects' brief was "Modern in design, frugal in operation and evangelical in purpose", hence the chief features are external and internal glazed walls stencilled with quotes from scripture. A look around: First expect a ten minute film, in part recalling how this site was firebombed out of existence in 1941, followed by a soft soap account of the organisation's good works around the world. Then expect a tour of the building, from the glass walled conference rotunda to the General's glass walled office where his desk can be seen by every passer by. The chapel space is beautifully simple, a small room leading down to louvred windows which reflect the sky and clouds rather than the uglier buildings opposite. Expect the tour to end in the cafe, of course, and there might even be a brass band to entertain outside.
Building: Escaping the City now, here's an unlikely survivor that probably merits an entire post of its own. Victorian passengers waiting for trains at Peckham Rye luxuriated in a huge room above the ticket hall, which eventually fell out of favour and became a billiard hall, which eventually fell out of favour and was closed. A few years ago the windows facing the platform were unbricked and a major restoration began, which still has some way to go - the floor is still imperfect in parts and the walls and roof very much looking their age. Most recently the main stairwell has been reconnected, topping old with new, and fresh access permits many possible future community uses. A look around: It wasn't just Open House luring visitors inside, the walls of the waiting room were also emblazoned with historic photos of Peckham Streets from the 1890s to the present day sourced from Southwark council's collection. These were wonderfully evocative, especially so if you actually live here, hence the room was packed out, not just with older history buffs but with trendy bearded youth. Many paused for some tea and cake and a sit down, which was apt, as this marvellous room briefly reverted to its original purpose.
Buildings: Beside the Regents Canal in Hackney, this unique rooftop project hosts a series of experimental architectural structures with a focus on innovation, sustainability and recycling. Four different eco-buildings perch atop Columbia and Brunswick Wharf, the kind of complex rooftop cityscape a rogue TV detective might normally chase a criminal across. This year's addition is a scaly silver framework resembling a ventilation duct, encased in stapled cardboard 'tiles', which conceals a tiny sheltered garden at its upper level. A look around: Poking around old warehouses is fun enough, but exploring roofspaces via diverse atypical stairs was quite an adventure. The only way to reach two of the houses was to descend a long external ladder from one roof to another, while temporary wooden stairs in a separate building eventually narrowed to a tiny vantage point within the aforementioned silver twirl. Yes, of course there are beehives up here. Yes, I bet the parties hip Hackneyians throw up on the roof are quite something.
Building: I'll finish off with one near my home, a former dog biscuit factory beside the Limehouse Cut converted into residential units long before this was cool. The conversion was done poorly, or so the latest owner of Unit 4 Block B believed, so he brought in architects to spruce up his cavernous warehouse-style space. They did a proper revamp using a lot of reclaimed materials, adding a master bedroom above the living space, which doubles up as the perfect shooting gallery when TV crews or Hollywood directors come to visit. A look around: It's surely obligatory to poke round someone's home on Open House weekend, if only to go "ooh, I like the way they've done that, I wonder whether it would work in my place?" or to erupt in a seething fit of jealousy. For the majority of the group I walked round with it was definitely the former, ogling the rough surfaces, eyeing up the bathroom sinks and coveting the Crittall windows. Divided up differently you could easily squeeze four pleb-sized flats into the same space, and the heating bill must be on the high side, but it's amazing how desirable a dog biscuit bakery can become.