To some in this city, turning Alcatraz back into a prison would be a crime. “The Rock” closed 62 years ago, and San Francisco has channeled the public’s macabre fascination with life inside the notorious prison to turn it into one of the city’s top tourist attractions.

President Donald Trump announced he wants to reopen Alcatraz, the prison near San Francisco that was featured in prominent movies and held famous criminals. The move was unexpected and shocked many. The prison is a museum and hasn’t been in operation for decades. But Trump wants the prison to “house America’s most ruthless and violent offenders.”

Experts say the federal government would have to overcome enormous hurdles to turn Alcatraz back into a prison.