From the Statue of Liberty to the Grand Canyon, the shutdown of large parts of the US government will bring disappointment and disruption to millions of tourists - many of them British.
A leading travel agent, Haydn Wrath of Travel Nation, said: "This is a classic example of how brinkmanship can produce a ridiculous lose-lose solution. Our customers, along with all other British tourists in the USA, will be mystified and disappointed as they see their carefully researched and planned trips to this fantastic country wrecked."
The US Congress row over funding and health care will have the most concentrated tourism impact on the American capital. Barricades started going up shortly after midnight, local time, to block access to the Lincoln Memorial and the war memorials of Washington DC.
All 17 Smithsonian museums in the capital, as well as the National Zoo, are closed indefinitely. On an average October day, 100,000 visitors would be expected to the Smithsonian Mall - with the Air and Space Museum, the Museum of American History and the Natural History Museum the most popular attractions.
The Washington Monument, the 555-foot symbol of the capital, is currently closed due to damage from an earthquake two years ago.
In New York, Liberty Island - location for the Statue of Liberty - will be off-limits for the duration of the shutdown. The American Indian Museum in lower Manhattan is also closed because it is part of the federal-funded Smithsonian.
In Boston and Philadelphia, the key locations in the story of American independence will also be closed, including the Bunker Hill Monument in Boston and Independence Hall in Philadelphia.
The closure of so many key attractions is likely to put pressure on the museums and galleries which are open, as tourists search for alternatives to their planned visits.
October is a popular month for visiting America's greatest National Parks, including the Grand Canyon, Yellowstone and Yosemite. Workers at these locations were told to turn up for work at 6am, spending no more than four hours in securing property, re-directing emails and clearing their desks.
During an average October, the 400-plus elements of the US National Park system welcome nearly 25 million visitors.
There is some hope that tourists who have planned the trip of a lifetime to the Grand Canyon may still be able to visit. When the US government last closed down, 18 years ago, the state of Arizona paid to keep the most popular areas of its flagship National Park open. Helicopter tours of the Grand Canyon will continue.
Queues for US immigration could get even longer than usual. The 1.8 million passengers who fly from American airports each day may face extended lines for searches if the Transportation Security Administration makes staff reductions.
Most British holidaymakers whose trips are disrupted have little hope of compensation. Those who have booked package holidays focused on specific locations may be entitled to a full or partial refund, but independent travellers who make their own arrangements have no such entitlement.
There could be benefits for tourists who bid their time before going west, according to Haydn Wrath of Travel Nation: "The only winners will be those who travel after everything has re-opened, as dollars will likely be cheaper following the impact this will have on the US economy."
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