When the portcullis is lifted up, another one appears. A DC 12 Wisdom (Perception) check notes that the opening for the portcullis in the ceiling is much wider than needed. A DC 8 Intelligence (Investigation) check reveals that it is 5 times wider than needed. A DC 10 Wisdom (Perception) check reveals a large pile of wood and metal about 40′ down the hall from the portcullis. When the portcullis is lifted up, which requires a DC 13 Strength check, as soon as a target tries to pass under it, another portcullis appears just behind it. This portcullis is in all respects identical to the previous one. This happens a total of 4 times. In order to pass, 5 portcullises have to be dealt with. When the new portcullis appears, a DC 14 Wisdom (Perception) check lets the target notice that the pile of wood and metal has gotten a little smaller. A 5 foot section of a portcullis has 20 hp and AC 15. Propping up a portcullis requires lifting it then using something to hold it up. It requires a DC 12 Dexterity check to properly place the prop. If this check fails, the portcullis will fall. The target propping it up must make a DC 10 Dexterity saving throw or take 1d6 bludgeoning damage. An aura of transmutation can be detected on the portcullis with detect magic or a successful DC 14 Intelligence (Arcana) check. Dispel magic or a DC 16 Intelligence (Arcana) check dispels the trap. Any portcullises that have already been created are unaffected.