The buildings in the Tempest Stronghold, apart from the Dragons Keep and the Training Camp, increase the stats of the Tempest Dragons and the Stats of the Tempest Cabals when they march with one or both of the tempest Dragons.
Like in the Skythrone Outpost, the Steelshard Caverns and the Luna Plains, the Tempest Stronghold has a library that increases speed, a depot that increases range, an academy that increases ranged damage, a forge that increases melee damage, a greenhouse that increases life and a cathedral that increases defense.
Upgrading requirements
Here are the upgrade requirements and power gain for one of the Tempest Stronghold buildings:
The upgrade requirements, power gain and the rest of the stat increases can be found here: