The Fortified Zone comprises Floors B21 to B25 of the Den of Trials, and it is based on the scenery and Enemies of the Fortress Area of the Drablands. It is initially unlocked and accessed by completing the prior Frozen Zone; if all three Links have already unlocked the Fortified Zone, they can access it directly by standing on the fifth Triforce Gateway in the Den's hub Level.
Each Floor of the Fortified Zone is an octagonal platform with a solid stone ground, and several ledges along each of the non-diagonal edges that act as walls. The Links first appear in the south corner, and a Triforce Gateway appears in the north corner once all Enemies on the Floor are defeated. On Floor B21, the Links are provided with a Gust Jar, Bombs, and a Bow; four Arrow Traps on the ledges around the Stage will automatically start firing Arrows once the Links select their Items. The Floor contains four unlit Braziers sitting in the Arrows' paths, and two lit Braziers in front of the northern and southern Arrow Trap, which quickly causes a chain reaction leading to a flurry of Fire Arrows across the Stage. This trap can be avoided if the Link wielding the Gust Jar extinguishes the two lit Braziers before all Links select their Items, though the Braziers will reignite after one minute.
Floor B22 has five Mini-Margos that spin around the Stage; two stacks of two Mini-Margos spin in a clockwise circle near the Floor's edges, momentarily stopping at the north and south corners, while the fifth Mini-Margo spins non-stop in a smaller, counter-clockwise circle. In the center of the Floor are two Bomb Flowers and a dark Keeleon hovering around, which spews black fireballs that curse the Links on contact. This Keeleon is at a height of two Links, requiring the heroes to form a Totem or throw Bombs to attack it. When either the Keeleon, or the four outer Mini-Margos, or the single inner Mini-Margo is defeated, a second dark Keeleon appears at a greater height.
Floor B23 begins with a Beamos on a pedestal in the center of the Floor, and the four dark Hinoxes standing on the ledges around the Floor's perimeter. The Hinoxes can easily be knocked off of the stage with a single hit, but if the Beamos and both Gimos are defeated first, then the dark Hinoxes will drop to the ground and begin giving chase to the Links. Floor B24 features two waves of dark Sky Soldiers, which have strong defenses and will chase the Links aggressively. They are perhaps most easily dispatched by luring them toward one of the Links, while another uses the Gust Jar from the side or the rear to blow them off of the Stage.