The diplomatic Viennese waltz at the Iran talks

Tucked away behind some trees is a serene rooftop garden at the luxury Viennese hotel hosting the Iran nuclear talks. There negotiators working round-the-clock can relax, hidden from the hordes of cameras below.

Next to mock Grecian statues, discreet waiters bring drinks and snacks while a small fountain splashes, providing a calm oasis away from the elegant, yet stuffy rooms of the Palais Coburg where the hard work of reaching a deal is being done.

Just metres below is a huge white tent erected on a pedestrian walkway to house some 565 accredited journalists from around the world. The two worlds rarely meet, only for choreographed picture opportunities.

Temperatures have soared in the Austrian capital this week as a heatwave hits Europe, and Vienna's famous squares and coffee houses have overflowed with sun-seekers soaking up the unique atmosphere in the city of Mozart and the painter Gustav Klimt.

But for the American and Iranian delegations seeking to nail down a deal putting a nuclear bomb beyond Iran's reach, there are few places among the magnificent 19th century and art deco buildings where they can safely avoid the media scrum.

Over the past weeks Vienna has become a home-from-home to many of the experts gathered from the US, EU and Iran who are doing the heavy lifting to reach a complex, highly technical and politically sensitive accord.

Skype and FaceTime accounts have gone into overload, as they try to keep up with birthdays, end-of-school year celebrations, and just the everyday news from home about bills that need paying, repairs that need doing.

- No more schnitzel! -

Some long for a change of scenery, and even of menu. Vienna schnitzel and bratwurst may be a local delicacy, but not when you're having it night after night.

While many of the foreign ministers have come and gone, US Secretary of State John Kerry, still walking on crutches after breaking his leg, is here for the long haul.

Asked earlier if Kerry and his team may leave Vienna and return after the July 4th celebrations, a senior US administration official joked: "If all of the political directors and experts leave here and take a break, they probably will never come back."

The official praised the teams as "tremendous heroes."

"People work from seven in the morning until midnight, if not longer, virtually every single day. They haven’t seen their families. They haven’t seen their children."

One Western official given a rare day off, cycled to Bratislava, the capital of neighbouring Slovakia some 70 kilometres (40 miles) away just to clear his head.

The negotiations have "become a bit of an obsession," joked another Western official, adding "it's enough to drive you mad."

EU deputy foreign policy chief Helga Schmidt, as well as US Under Secretary Wendy Sherman met with their Iranian counterparts from 9pm Thursday night to 3am Friday morning -- non-stop.

On balmy evenings strains of music-- what else but Viennese waltzes? -- waft from packed beergardens, where occasionally a delegation can be seen enjoying a rare moment of downtime on the banks of the river Danube.

Two hundreds years ago exactly, the city played host to the Congress of Vienna when the Emperor of Austria, the tsar of Russia as well as the kings of Prussia, Denmark, Bavaria and Wurttemberg reorganised the borders of Europe following Napoleon's defeat at Waterloo.

Today, eager once again to earn a place in the history books, Austrian authorities have been lavish in their hospitality. In the vast media tent, free ice-creams, coffee and water have been on hand.

A mini-crisis may be looming though if the talks drag past Tuesday's new deadline.

The city's authorities ordered some 2,500 typical round Viennese chocolates known as Mozartkugeln to give to reporters ... and they have already run out.