Doors in Udgaard

There are eight? tower guards in Udgaard. I was recently fighting a bard and necromancer in Udgaard, and they went into these towers, closed the door from the inside, and I couldn't open it from the outside to get the treant and call of the wild in, which resulted in me fighting without them. Later, after the opposition left, I tried using several different keywords, but nothing seemed to work. "Close (direction)" from the inside of the tower works just fine, but nothing seemed to work from the outside of them. Am I missing something?