The new U.S. Embassy in London has been officially unveiled, with staff set to move in next month.

The new Embassy cost $1B to build, making it the most expensive embassy in the world, and ends the 225-year association of the U.S. with its previous home on Grosvenor Square, Mayfair, where Gen. Dwight D. Eisenhower was headquartered during the Second World War.

The new building is in Nine Elms, close to the famous Battersea Power Station. Take a look inside.

$1B to build and twice as big as its previous home

The U.S. government played the London property market pretty well. The new embassy cost around $1B to build, but the entire project was funded by selling the former embassy and the former HQ of the U.S. Navy, both on Grosvenor Square. The 12-storey glass cube is 518K SF, twice as large as the previous embassy.

Getting medieval on you

Obviously security at the new embassy is paramount — and for that reason it will be surrounded by the first moat built around a Central London building since the medieval period, though it is not yet filled with alligators/sharks. The white concrete plinth beneath the building is supposed to be impervious to attack from beneath, and the northern edge of the site is protected from the road by bollards.

A spy-proof building

The focus on security extends to the architect and materials used. The architect, Kieran Timberlake, was required to achieve numerous security clearances and all of the building materials used originate from the U.S. to ensure they could not be bugged or compromised in any way.

The offices are not exactly cutting edge

The images of the working environment for the staff at the new building suggest the U.S. government did not get the memo about fashionable working environments — no exposed air conditioning or elegant design here, although the glass cube does let in plenty of natural light.

A little bit of American flora in London

There is plenty of greenery in and around the building, with internal gardens supposed to evoke different regions of the U.S., although the Financial Times' architecture critic Edwin Heathcote compared them to airport smoking lounges.

The building is designed to be green in a different way in that it is carbon-neutral. The roof is covered in solar panels and the moat doubles as a rainwater run-off reservoir.

Open to the public, to a degree

While security was a big part of the building's design, it has also made an effort to be open to the public, with the north side of the site accessible to the public in the form of gardens. The grass has not grown yet and the moat is not full.  Here is what it will look like next year when nature has taken its course.