In general, beyond the odd bit of decorating and DIY, we rarely pay much attention to the buildings in which we spend so much of our lives. The London Open House weekend, on 20 and 21 September, aims to open the doors, and thereby our eyes and minds, to the architecture all around us. This annual event, organised as the London equivalent to the heritage open days that take place across the country, gives visitors free access to more than 500 buildings across the capital, many of which are normally closed to the public.
From Barnet to Bexley, Ealing to En-field and Hounslow to Haringey, not to mention the City and Westminster in between, a multitude of buildings are being revealed. These include the very old (such as the Guildhall in the City) and the ultra-modern (such as the Lloyd's Building). Banks, bunkers, cinemas and cemeteries: you name it, Open House has persuaded the owners to let you in. Even England's top venue for arms sales, the ExCeL Exhibition Centre in Newham, is involved - so if the police prevented you getting anywhere near it the other week, now's your chance to take a look.
The range of buildings on offer reflects more than London's history and the ever-increasing possibilities created by developments in technology. It also shows how a building's form is, to a significant extent, determined by its function. According to architectural etiquette, different types of building have been considered appropriate for different uses.
But architectural diversity also expresses cultural diversity. As well as St Paul's Cathedral, London is home to the East London Mosque in Tower Hamlets, the Buddhapadipa Temple in Merton (a complex of buildings including a Buddhist Theravada temple in the Thai tradition, one of only two outside Asia) and the Shri Swaminarayan Mandir in Brent (the first ever traditional Hindu mandir to be constructed outside India), each of which is open over the weekend. New buildings also reveal changing lifestyles. Included in this year's Open House is the Iyengar Yoga Institute in Maida Vale, one of the first purpose-built yoga centres in Europe. Clearly demonstrating how the use of a building informs its design, yoga's philosophy is translated into the crisp simplicity of the interior, with light pouring in through a grid of square light-wells in the ceiling.
The variety of shapes and styles, particularly in central London, also testifies to the way the city has never been subject to the kind of urban planning that has had such a lasting effect on Rome, Lisbon or Paris. This is not from a lack of ideas: within days of the Great Fire in 1666, several plans for rebuilding the city were laid before the king. These ambitious schemes, including one by Christopher Wren, sought to replace the ramshackle form of the medieval city with an ordered, gridlike design.
If Charles II had been as powerful as Louis XIV, London might well have been resurrected according to such a plan. But lack of finances, the need to restore the city quickly and, more than likely, a desire to recreate the familiar rather than risk changes conspired to ensure that the city was rebuilt very much along the same lines as before. And even though laws were passed with the aim of regularising the fronts, heights and materials of buildings (not least in an effort to prevent another fire on the same scale), England's peculiar property rights made it very difficult to keep the individual builders in line. Following the Great Fire, as with after the Blitz, the approach to restoring London was patchy rather than well planned.
Wren, many of whose designs are included in London Open House, once said that building "ought to have the attribute of eternal" and should there- fore be "the only thing uncapable of new fashions". For this reason, he preferred the classical style - columns, capitals, lots of white stone.
But the myriad buildings involved in the Open House weekend prove that architecture, like any cultural product, reflects the changing preoccupations and values of society. And fashions come back in, even if in a slightly altered form. In the crypt of St Paul's, Wren may well turn in his grave as Open House's tour of Paternoster Square gets under way. The new development, right next to Wren's cathedral, is finally nearing completion more than a decade after Charles II's namesake and heir, the Prince of Wales, intervened in an attempt to prevent another modernist "carbuncle" from being built. The result is a combination of modern glass and concrete with a heavy dose of classicism echoing the cathedral.
In one of his tracts on architecture, Wren wrote about how "architecture has its political use". It is certainly possible to trace the changing seat of power through the history of architecture. When first built, the many churches included in London Open House dominated the city's skyline, expressing in a highly visible way the control and influence the Church sought to impose on city life. Today, a number of London's churches lie dilapidated and dependent on Lottery money for survival, superseded by the looming towers of big business. Competing with each other for attention, these palatial offices proclaim the power of the "new religion", capitalism - their extensive use of glass claiming transparency and openness for the corporations inside.
By giving the general public access to buildings from which they are usually excluded, this event reveals just how much architecture controls our movements and experiences (who we mix with, what facilities we have access to). It's no accident, for example, that in blocks of flats and office towers, the most prestigious and expensive suites are at the top.
In prising open the doors to so many different buildings, London Open House succeeds, even if for two days only, in subverting one of the many uses of architecture: to keep us out.
For further information about the London Open House weekend, visit www.londonopenhouse.org  or phone 09001 600 061