The Serpentine Gallery in Hyde Park has just doubled in size - taking over an old gunpowder store nearby. This was built during the Napoleonic wars "in case of foreign invasion or popular uprising". It was a time when our rulers were terrified that the French Revolution might be contagious, and felt they needed a ready supply in the heart of the capital.
The MOD only relinquished its hold in 1963, when it handed the store over to the park authorities. In recent years it has been host to less explosive materials, such as the flagpoles that line The Mall when foreign heads of state come to dine with the queen.
The glitzy opening of the new gallery in September was attended by A-listers of the ruling class - the likes of Roman Abramovich, Boris Johnson, Pippa Middleton, George Osbourne, Jemima Khan and Jeremy Clarkson. Some artists even turned up.
But what has attracted the most attention is the flamboyant extension to the Grade II listed building, for which the star architect Zaha Hadid was commissioned.
Her work has become very fashionable in the last decade. She has benefited from the boom in "iconic" buildings - one driven by the belief that spectacular architecture can perform miracles of regeneration for cities.
Hadid's studio does not seem picky about who it works for. Recent projects include the Heydar Aliyev cultural centre in Baku, built in honour of Azerbaijan's former president-dictator. Up to 60,000 people were evicted from their homes to make way for this gentrification project.
Hadid's buildings are often spectacular, if not always functional. They are trophies. And they are usually built from scratch, which makes this project a bit of an exception.
The makeover of the gunpowder store has come in for some harsh criticism. Expectations were high as 14.5 million pounds was lavished on the project. But I'm mystified as to where the money went. It's quite small, and a bit shabby.
The Guardian's critic described it as "like a wedding marquee battling with a stiff breeze". He wasn't voicing a horror of experimentation. On the contrary, he felt that Hadid's approach was corporate and conservative - her trademark style evoking a "space-age sanitary wares showroom". That's certainly the feeling I had.
The extension also fails to engage with its 208-year old neighbour. It feels like a parasitical growth. The only doorway linking the two is for kitchen staff!
It is revealing that this multimillion pound outhouse won't display any art. It's going to be used for fine dining, corporate events and lectures. It seems aimed at those with deep pockets who wish to bask in the aura of art, but not take the trouble to engage with it.
When small arts projects around Britain are having their funding slashed in the name of austerity, who coughed up the funding for this overpriced ornament? We seem to be moving towards the US model of rich philanthropists donating to their favourite institutions.
Cultural workers are deeply uneasy about this, as they feel donors will increasingly determine what gets made and displayed. More challenging work, and less glamorous institutions, will get sidelined.
The Arts Council put in just 18 percent of the funding for this new gallery. The rest came from wealthy benefactors. In fact, the Serpentine says the project was only made possible because of a huge donation from the Sackler Foundation - which has also given its name to the building.
Most of this foundation's money comes from the pharmaceutical businesses run by Mortimer Sackler, who died in 2010. The Sackler family made a fortune from one of the most infamous (and profitable) drugs in recent US history - Oxycontin. This is a narcotic for patients with severe pain. However, it also became very popular - and very addictive - as a recreational drug.
It's like heroin, but without the needles. And it's available on prescription. In some parts of the US abuse was so widespread that doctors refused to prescribe it. And break-ins at some chemists by Oxycontin addicts became so common that they refused to stock it. In recent years annual sales have averaged 2.6 billion dollars.
Despite all this, I do recommend a visit. Entrance is free, it has a great location in Hyde Park, and the opening exhibition by Argentine artist Adrian Villar Rojas is engaging and irreverent.
Serpentine Gallery, Kensington Gardens, London W2 3XA