Inside the 'No-Go Zone': Searching for Answers at Japan's Fukushima Nuclear Plant

The Fukushima Daiichi Power plant is the site of one of the worst nuclear catastrophes in history, and it's still grappling with possible radioactive water leaks almost three years after a devastating earthquake and subsequent tsunami triggered a meltdown.

On March 11, 2011, a 9.0-magnitude earthquake, the largest ever to hit Japan, and the tsunami that followed, engulfed entire villages. Giant waves flooded the Fukushima plant, knocking out power and causing a meltdown that spewed radiation across the countryside and into the ocean.

At first, Tepco, the plant's operator and the largest energy company in Japan, downplayed the severity of the disaster, and critics have since accused the company of withholding vital information about the plant. Now, at the start of an unprecedented and treacherous cleanup, Tepco agreed to open its doors and show what progress the company has made.

The plant is surrounded by a 12-mile evacuation zone, teeming with radiation hot spots. Deep in fallout territory, masked guards man street corners, only allowing people with official government permission to pass. Inside what the locals call the "no-go zone" are ghost towns, abandoned and overgrown.

It looks like a post-apocalyptic landscape. In all, 80,000 people were forced to evacuate their homes, and most won't be able to return for decades. For some, maybe never.

Tepco said it has a plan in place to stop future radiation leaks. It has also increased defenses for the next natural disaster with new technology that will ensure backup power and supply water to cool reactors during an emergency.

"Nightline" went on a journey to examine the fallout of the Fukushima power plant meltdown, and was given rare access to the plant and its surrounding evacuation zones. Watch ABC News' Cecilia Vega and "Nightline" producer Nick Capote's full report HERE: