Yes indeed......
Some say there is no known way of detecting secret centrifuge facilities for enriching uranium because these can be smaller than an office building, would easily fit into an underground tunnel, consume very little electricity and release almost no thermal or chemical emissions..so makes them hard to find.
No matter how extensive verification will end up happening in the N.K. it’s going to be a long process.
Underground systems have to be ventilated. There will be a heat signature someplace where the air is being discharged after passing through the facility. They can be found and likely we already know where they are.