Little is known about the complex near the Natanz nuclear facility, but it is estimated it is buried almost 100 metres inside a mountain

Iran is secretly hardening a deeply buried nuclear site called Pickaxe Mountain — in open violation of its U.S. agreement. Here's why it can't be ignored.

Pickaxe Mountain has emerged as a major Iran nuclear concern, but questions remain over whether the facility is operational and whether a strike would achieve its goals.