I thought I had reached the threshold of liberty, but here was an impediment that threatened to be insurmountable.
But, if doors could not be passed, windows might be unbarred.

I remembered that my companion had gone into a door on the left hand, in search of a light.

I searched for this door.

Fortunately it was fastened only by a bolt.

It admitted me into a room which I carefully explored till I reached a window.