古北界

古 = 十 + 口 : Mnemonic symbol: at least on German maps, this character actually resembles a cloister.

Oh no! Gitta Giraffe (gu) found that the golden cross (十) broke off of the cloister (古) in the space station's living room (Ø3)! She skewers a mandarin (口) on top of the cloister so that she can skewer the broken off cross back on to fix it.

北 = 丬 + 匕 : A compass rose. In the Eiffel Tower, Beelzebub tries to build a compass. As a baseplate he uses a piece of wood, on which he sticks the north pike of a compass rose. On the south pike he balances a ladle, which is supposed to adjust itself to earth's magnetic field.

界 = 介 + 田 : Joan of Arc wants to leave this world and sets up a rocket launch field in the elevator's bathroom. The field looks like a normal crop field, except that there's a rocket in the middle and that the Joan of Arc marked the boundary with white and red tape.