Sentence:  Why did God make me an outcast and a stranger in mine own house? The shades of the prison-house closed round about us all: walls strait and stubborn to the whitest, but relentlessly narrow, tall, and <WSD>unscalable</WSD> to sons of night who must plod darkly on in resignation, or beat unavailing palms against the stone, or steadily, half hopelessly, watch the streak of blue above. 
Meaning of the word marked with <WSD> tags:  Not scalable, that cannot be climbed.