Artifacts found in the caves and Catacombs under Marcuria, by both Zoë Castillo and April Ryan. Both eggs emit a steady golden light, and appear to be clockwork as they produce a mechanical ticking noise.
Zoë finds one egg attached to a staff on the underground beach, being used as a light source. When it is placed on the machine connected to the giant water wheel, it produces the four-tone melody used in several puzzles in the caves, and concentrates the flow of power to the wheel. Its light also reveals the symbols on the wall at the end of the tunnel. April discovers the second egg hidden in a sarcophagus in the Catacombs, and uses it as a key to open the gates into the deeper caves that eventually lead to the Dream Chamber.
Whatever the eggs are, they are clearly linked with the mechanisms under Marcuria - machines April says are out of time and place - which, coupled with the presence of an egg in a sarcophagus, suggests that those buried in the Catacombs were their original makers. April comments that the eggs look like they combine "magic and technology...like those Azadi machines. But this thing is very, very old." The Grubbers don't appear to know what they are for, hence their use of one egg as, effectively, a glorified lantern.
Obtained from the Grubber's staff and from the sarcophagus.