The words that can be used for synonym is grotto...
grotto:
→ <span>a small picturesque cave, especially an artificial one in a park or garden
</span>→ <span>an indoor structure resembling a cave.
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Opening is a synonym for cave, a cave is a grotto.</span>
Setting is the answer because it is describing the place
The part that says: "Within these last 19 months at least 45 satellites have circled the earth".
