Fortresses are intimidating labyrinths full of nasty traps and powerful monsters, the most notable being the Eggplant Wizard. Pit must travel through these dungeons to acquire the Three Sacred Treasures' Sacred Caskets from the guardians in each fortress.
Pit can acquire Check Sheets within the fortresses, and merchants will carry Pencils and Torches so that Pit can track his progress on the map; however, these items will disappear from his inventory once he leaves the fortress.
There are two primary hazards in a fortress. First, many rooms contain ditches filled with lava or acid, and careful platforming is required to successfully navigate this. Secondly, many corridors are guarded by spikes that slide in and out of blocks located along the floor and ceiling. These traps follow a set rhythm, but Pit will still need to be quick on his feet to avoid getting impaled.
By freeing Centurions with Mallets, Pit can make the battle against the fortress guardian easier. Also, the antimagic aura of the fortress will prevent the Sacred Bow, Fire Arrows, and Protective Crystals from working, no matter how high Pit's Hit Points are. They'll return to working status as soon as he leaves the fortress.
Merchants in Of Myths and Monsters will have higher prices than in other areas. Unlike the original Kid Icarus, Pit's special weapons will work here as long as he meets the HP requirements.