It lies at the very heart of an enduring, hostile relationship.
To Americans, it was a bitter betrayal – a group of former allies-turned-extremists who took 52 American patriots hostage for more than a year.
To Iranians, it's a symbol of American oppression – a "Den of Spies" where U.S. agents had been monitoring and plotting against Iran for decades.
ABC News was given unprecedented, unrestricted access to the former U.S. embassy compound where Americans were taken hostage in 1979, a process that led to the severing of ties between the United States and Iran – a wound on their collective psyches that continues to this day.
Inside, it's part museum, part conspiracy theorist haven. A mural painted in the stairwell depicts planes striking the World Trade Center towers – and the Afghanistan and Iraq wars that followed – with a clear suggestion that American "agents" plotted the attack themselves, in order to wage war on other countries."
A tour guide, polite and well-spoken, insisted that the entire 9/11 attack was scripted.
"It was all a Hollywood production," he told me.
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He wasn't laughing. The look on his face showed he believed every word of what he'd said.
Upstairs, the original steel safe door marking the entrance to the intelligence side of the embassy still exists.
"Put your hand on the wall," the guide tells me, as he slams the door shut. There's no vibration.
"See, the Americans put so much thought into this building that they even made it so that the door would slam shut without vibrating the rest of the building."
Nearby, Iranian officials have preserved the embassy's famous "glass room" whose walls and ceiling are made entirely of a flimsy, plastic-glass material. An eerie wax copy lookalive of Ambassador William Sullivan, the last serving U.S. ambassador to Iran, is propped on a chair inside, complete with white hair and 1970's, Mad-Men style business suit.
Other rooms have photo exhibits and sculptures depicting American foreign policy defeats since the Islamic Revolution in 1979.
In nearly every room, original materials seized during the embassy takeover have been meticulously preserved.
"This is an original paper we found," my guide explains, holding up an aging piece of paper that reads "diplomatic pouch certification and receipt."
When embassy staff realized the compound was about to be overrun, they set off on a desperate mission to destroy and shred as many official documents as they could. Many of those original paper shredders are still on display, along with old computers that look like Atari machines of the 1980's.
In one of the corridors, Hossein Shaykholislam, looks into the glass room through its door.
"This is the first room I entered," he says about the day he and other militants stormed the embassy, his voice hinting at a nostalgia of years gone by.
Shaykholislam had been studying at Berkeley University in the late 1970s and returned to Iran during the revolution. Due to his command of English, he became a de facto spokesperson for the students, often translating directly back and forth with the hostages.
"At the beginning, it was tense" he recalls.