Iran may be secretly building a nuclear weapon inside Pickaxe Mountain, a site left untouched by US airstrikes — a small but dangerous risk for the world.

• Pickaxe Mountain is the deep facility the US did not hit during Operation Midnight Hammer or the latest round of strikes.
• There's an estimated 8% chance Iran suddenly announces it has a working nuke and uses it to make demands.
• If Iran reveals a weapon, a US attempt to shoot it down could spread radioactive fallout over Europe and kill many people.
• The site's depth is the problem — it may be beyond the reach of even the B2 bunker-buster bombers used elsewhere.

Outlook: Pickaxe Mountain stays the key unknown, and pressure to strike or monitor it will likely grow in the coming weeks.