On Nov. 4, 1979, a group of young Iranian activists broke into the U.S. embassy in downtown Tehran, captured virtually every American working there, and began one of the worst diplomatic crises in American history.

Though the 66 hostages were eventually released, the 14 month-long ordeal poisoned the already strained relations between the United States and Iran. The hostage crisis was a humiliating and grueling time for President Jimmy Carter, and it gave many Americans their first glimpse of Islamic radicalism.

For Ayatollah Khomeini and his fellow Iranian revolutionaries, the capture of America’s embassy and its diplomatic staff was a hugely symbolic victory over “The Great Satan.”

Thirty-five years later, many analysts believe the ill-will from that crisis echoes to this day. Former State Department official John Limbert, who was also a hostage, says that when Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif sit down to negotiate Iran’s nuclear program, the decades-old crisis lingers as a “ghost in the room.”

But what became of the former American embassy?

While filming last year in Iran for a series of NewsHour reports on how western sanctions are impacting that nation, we were granted rare permission by the Iranians to see inside the former U.S. embassy in downtown Tehran.

Here’s an inside look at what the hostage-takers referred to as the “Den of Spies”: