A Fortress is an intimidating labyrinth of nasty traps and powerful monsters, the Eggplant Wizard being the most notable. Pit must travel through these dungeons to acquire the Three Sacred Treasures' Sacred Caskets from the guardians in each fortress. Unlike other areas, chambers stay unlocked here, and Pit should feel free to abuse the Stores, Hot Springs, and Hospitals that he'll encounter here. There are no Sacred Training Chambers, Sacred Chambers, or Treasure Chambers (nearly every room could be considered to be an Enemy Lair, though).
Somewhere in the Fortress, Pit can find a Check Sheet, and merchants will carry Pencils and Torches so Pit can track his progress on the subscreen; however, these items will be destroyed when he leaves the fortress.
There are two primary hazards in a Fortress. First, many floors may be flooded with lava or acid, and careful platforming is required to successfully navigate this. Secondly, many corridors are guarded by sliding spikes. These pointy protectors slide in and out of specific blocks. There's a specific pattern to the automated traps, but Pit will still need to be quick on his feet to avoid getting impaled.
By freeing the Centurion side-kicks with Mallets, Pit can make the battle against the Fortress guardian easier. Also, the antimagic aura of the Fortress will prevent Pit's weapons (Sacred Bow, Fire Arrows, and Protective Crystals) from working, no matter how high his Hit Points get. They'll return to working status as soon as he leaves the Fortress. When descending into a new room from a ladder, Pit will normally let go and fall into the room. However, by holding up on the controller, he'll hang onto the last rung, giving him time to scout the room before dropping into it.
It's possible for Pit to engage the Sacred Guardian as an Eggplant. This is tantamount to suicide, of course, as the door closes behind Pit. Any freed Centurions will be able to fight, but if Pit runs out of Centurions, the angel is doomed.
Kid Icarus: Of Myths and Monsters
Merchants in Kid Icarus: Of Myths and Monsters will have higher prices than in other areas. Unlike the first adventure, Pit's special weapons will work here as long as he meets the HP requirements.
Kid Icarus: Uprising
Although quite different from the traditional Fortress, a location called the Reaper Fortress serves as the primary destination of the The Reaper's Line of Sight and houses the boss battle against the Big Reaper. In addition, Gaol's Castle can be considered similar to a Fortress as well.