Eesfet Oon-m'Aa Poo (Location)
A First Civilization ruin accessible via the secret passage in the Great Sphinx, after you've completed all the Stone Circles.
You'll need 50 silica to activate the mechanism here. However, there are four chunks of silica in this chamber, that you can scan for.
When you have 50, activate the central pillar.
This completes the location, and launches the most comprehensive of the retransmissions.
This also unlocks the Isu Armor.
The armor doesn't actually *do* anything, but it is pretty cool.