Sentence:  It was the Lost Oasis, the Oasis of the <WSD>vision</WSD> in the sand. […] Deep-hidden in the hollow, beneath the cliffs, it lay; and round it the happy verdure spread for many a rood. […] Yes, the quest was ended, the Lost Oasis was the Found! 
Meaning of the word marked with <WSD> tags:  Something seen; an object perceived visually.