The Applied Magic classroom is Penwick's largest and most adaptable space. Its tall, cross-gabled roof and sturdy stone walls create a chapel-like hall. The room is divided into five distinct areas. Students enter through the narrowest corner, where they hang their coats and leave their belongings during hands-on lessons. Two practice areas extend to the left and right, while the center serves as the main instructional space. Opposite the entrance stands the Professor's desk alongside chairs and desks, which are arranged into a more traditional classroom seating when theoretical instruction is needed. Behind the Professor's desk, a narrow staircase leads up into a storage attic.

Hidden at the end of the easternmost corridor of the third floor is the classroom for the Forgotten Arts, the most popular elective at Penwick. The classroom itself is as eclectic as its coursework, with newspaper clippings and 18th century hand-drawn diagrams covering the walls. Students are encouraged to touch and interact with any magical item they find in the room: all are student-safe, and anything accidentally broken can become another lesson. First years, beware: one of the most popular Penwick pranks involves convincing the more gullible children that there's a long-forgotten secret passage from this classroom to the library, for those who are brave enough to go looking for it.

Functioning as a storage area for most non-perishable class materials of all disciplines, the Storeroom is a treasure trove for both the curious and mischievous alike. Everything from defunct astronomy equipment to mildly cursed practice dummies can be found here. A truly gargantuan space, it's clear that someone put an extending charm or two on the room, once upon a time. This is also where the school's cleaning supplies are stored, so detention's most frequent flyers may be especially familiar with the space.

Dominating the center of the Dueling Theatre is a large glass dome, inside of which lies the main dueling piste, the field where duelists go head to head for the entertainment of the masses. The glass is designed to be one-way, so that the crowd can see in, but the duellists' side is left foggy and opaque to prevent distraction and interference. Depending on the type of match, the field will either be left bare or filled with various obstacles like magical plants and steep rubble. Large sets of collapsible bleachers surround the dome, which when folded serve as smaller pistes for practice. Four small antechambers serve as locker rooms for each team, each denoted by their house's sigil carved into the door.

Set apart at the far end of the third floor, the Faculty Wing is where Penwick’s professors retreat when lessons are done. The long, straight corridor is lined with tall windows and portraits of former staff who still offer their unsolicited opinions. Small apartments house each of the faculty members, with a couple reserved for housing important visitors. At its center lies a wood-panelled lounge where faculty gather for tea, marking, and the occasional heated debate. Students are strictly prohibited from entering faculty quarters with the exception of emergencies; however, they may be granted permission to enter the lounge.