There's a mountain in Iran that has been keeping intelligence agencies busy for years, and it just got a lot more interesting. Pickaxe Mountain, a suspected nuclear site near the Natanz complex, has seen a noticeable uptick in construction activity this year, according to a new analysis from the Center for Strategic and International Studies (CSIS).

The think tank pored over six years' worth of satellite imagery and found what it calls a "clear surge in construction activity" at the site, which sits about 140 miles south of Tehran. The underground facility is "likely" meant to be a safe haven for Iran's nuclear program, the analysts say. But here's the catch: the mountain is made of granite, which makes it a tough nut to crack. Even the Pentagon's "heaviest non-nuclear" bombs would struggle to penetrate it, the CSIS team reported.

The construction at Pickaxe Mountain appears to have shifted from active excavation to internal work and exterior reinforcement. But the analysts note that the "continuous construction" suggests the site isn't ready for enrichment work yet, if that's even its intended purpose.

This all comes after President Donald Trump threatened to attack the site in July, even though there was "no activity" there at the time. Trump said authorities were watching it closely and might take a shot "relatively soon." The U.S. already struck Iranian nuclear sites in June 2025 under "Operation Midnight Hammer," which damaged key facilities but left the deeply buried Isfahan site largely intact. Now, the Pentagon is working on a next-generation penetrator bomb designed to reach deeper underground targets, with prototype work starting last year.

Defense officials are also continuing to develop plans for decisive strikes on underground facilities, with a recent "planning sprint" focused on potential operations, according to CNN. The Defense Department didn't immediately respond to requests for comment.

Meanwhile, the International Atomic Energy Agency (IAEA) has been in the dark on Iran's nuclear program for more than a year. IAEA Director-General Rafael Grossi said Monday that the agency lacks access to information on Iran's declared stocks of low-enriched and highly enriched uranium (up to 60% enrichment) at facilities affected by the June 2025 attacks. He called this a serious nuclear proliferation concern that needs urgent action, urging Iran to cooperate fully and meet its obligations under the NPT Safeguards Agreement. Grossi also pushed for a return to diplomacy and negotiations.

So, what's the takeaway? The situation is fluid, with Iran seemingly preparing for something big underground, and the U.S. gearing up to counter it. The granite mountain might be tough, but the Pentagon is working on new tools to make it less of an obstacle. And with the IAEA unable to verify what's happening, the world is left watching and waiting.