It's hard to find less accessible places on this planet that have been built by humans. They are hidden dozens of meters underground and surrounded by so many concrete and rock massifs that perhaps only one army in the world can reach them. If anyone can, it's definitely the United States.

This is how military experts describe the three main targets of current American attacks in Iran – Fordo, Natanz and Isfahan.

The first of these, Fordo, is a nearly impenetrable fortress hidden deep in the ground. So deep that if you dug a hole all the way to it, a 12-story apartment building could fit inside.

That's why the Americans have long since begun developing a bomb called the GBU-57, which is the only one capable of penetrating all the way to Iran's Fordow, where Iran is likely enriching uranium deep underground.

But even American military specialists themselves cannot be completely sure that they will succeed in practice. Moreover, bombing Ford is associated with enormous risks.

Known unknowns and unknown unknowns

The US military concluded that a single bomb alone would not destroy the Fordo facility. To destroy the facility, the attack would have to come in waves, with bombers being dropped one after the other into the same hole.