The Iranians have had 47 years to negotiate. They chose death and destruction (for America, Israel, and themselves) at every point.
What does an Islamic Revolutionary theocracy, blessed with oil and natural gas, need with nuclear technology? They don't need it, they WANT it.
As far as underground hiding spots, if you can't blow them up, bury them ... after you suffocate them to death with copious amounts of napalm.
All underground facilities require means of ingress and egress for people, air, electricity, water, heating/cooling, dehumidification, etc. Every place an Iranian has dug into rock - tunnels, quarries, hills, mountains, landfills, mines, foundations, slabs, etc. If there is a hole in the ground, napalm it to suffocate personnel and bomb it shut. If there is an amusement park using more electricity than it should, bomb it. Most everything requires electricity to function ... the electrons will lead you to the enemy.