As medieval a setting this castle appears to be, Reed reasons that it is actually electrical. Maybe he can find an outlet and squeeze through it to escape, if he's not held back by any troublesome goblins.
Mister Fantastic gets through the outlet without suffering any electrical damage. After traveling south for two areas, he comes to a wall that has a pair of ventilation ducts. One is on Reed's left and the other is on his right.
Mr. Fantastic Health: 42/42 Mr. Fantastic Karma: 80