When Old London Bridge was finally destined for the knackers yard, one of the many replacement proposals would have seen two mighty bridges constructed side by side.
In the dim and distant past, when Battersea Power Station was more ruin than construction site, a proposal was shown off that would have seen the old building become a major football stadium.
When culture seekers walk along the south bank admiring the views and skateboards, they should do so under a giant glass and steel canopy weaving its way along the Thames.
What was officially known as the Metropolitan Sepulcher, but more widely as the Pyramid of Death -- was a proposed massive pyramid built on Primrose Hill, which would have stood a staggering 950 feet high.
Is it a plane? Is it a train? No, it's Railplace! Racing above the streets of London carrying passengers from city centre to airports, to Brighton, to Glasgow, all at unbelievable speeds.
Today where a classical Victorian hotel stands overlooking Trafalgar Square, there should be a massive white curved pyramid -- the Blob.
Where the confection of the MI6 building currently stands, there should be a gigantic tower block -- the green giant.
Had plans gone as planned, London Underground's Central line should look more like the Circle line running in a loop, not a long single line passing through the centre of London.
Had things gone according to plan, instead of an old power station full of art, there would be an outpost of Mars on the south-bank of the Thames.
Imagine a railway, working without steam, running on tall columns along the banks of the Thames -- for that was a scheme created to link Blackfriars with Charing Cross in the 1840s.
Rather than full of glassy offices and a testicle, the south bank of the Thames by Tower Bridge should be a neo-Venetian folly.
In the early 1970s, plans were announced to demolish a cluster of old buildings opposite Big Ben and replace them with a vast monolith covered in bronzed glass.
The Houses of Parliament, that impressive confection of gothic architecture should look a lot plainer -- in fact it should be Georgian in style -- had plans to erect a new building in the 1730s been carried out.
Thirty years ago, a plan was shown off to replace the main road running along Oxford Street with a giant flyover.
Westminster Abbey is getting a bit crowded someone once thought, with all these monuments to dead people cluttering up the place. What's needed is a great big extension, and a massive tower.