Athos still clearly remembered the power the storm cloud had during the battle in the fortress and wanted to add it to his defenses.
"Once this fortress is completed, it's going to take a full-grown dragon to bring down all those defenses." It was Athos' honest opinion after confirming all the layers of defenses the dwarves planned to create.
In addition to all defenses, the dwarves would build an underground shelter, but those would be plans for the future. The most that they would work underground in the near future would be the underground mine that was in the inner area of the first wall, behind where the fortress would be located in the future.
The cave built by the spirits and demihumans was still standing, but the dwarves had plans to further strengthen the cave walls and build support pillars to expand the tunnels even further.