The Pick Nails can be found in a room in the Egg Fish Chamber.
Collect 100 Rings
Rings are scarce in the stage, so avoid getting hit. To collect 100 Rings as quickly as possible, grab every one from the room the stage starts from. Head then out of the exit beneath the giant scorpion statue, and keep going straight until the Egg Snake Chamber is reached; pick up every single Ring there. From there, turn left and head toward the Snake Altar room. Upon entering, break the Wooden Container to the left, next to the cagedHalf-Fish, to reveal a Super Ring with twenty Rings. If everything is grabbed from this room, it is possible to obtain 100 Rings by gliding from the top of the pillars or by collecting the Rings atop the large central platform.
Find the Lost Chao
Play the Mystic Melody at the Ancient Ruin atop the large center platform in the Snake Altar room, and jump into the Warp Hole that appears. The player will then be transported to a room with a giant Weight lying in the center and a Warp Wall on the left. Dig into the Warp Wall, and the player will enter a similar room with another Warp Wall in the shallow hole on the floor. Break through the first Iron Container in the ground south of the far left corner, and hit the exposed Switch. Now dig into the Warp Wall in the floor to be transported to the previous room where the Weight is now suspended in midair. Beneath it is the lost Chao.
Get the 3 Gate Keys in 3:00
Since this stage is relatively small and circular, simply run around until something comes up on the radar. The points received from finishing early are substantial, so do not be afraid to use a Hint Box.
Clear Hard Mode
The first key is in a Cage at the end of the boundary hallway between the Egg Scorpion Chamber and the Egg Fish Chamber (but closer to the latter section). Destroy the Cage by standing close to it so the Kiki nearby will throws bomb at it, or pick up a Kiki's bomb and throw it at the Cage.
The second key is in the Snake Altar Room, inside the Warp Wall on the west side of the room. Unfortunately, a stack of Cages is blocking it. The player needs to fetch another Kiki bomb, but before that, smash the Wooden Container on top of the altar below the Warp Wall and the Iron Container in front of it. Otherwise, it will not be possible to get back up here while carrying a bomb. Once the player has a bomb, they should use it to blow up the Cages, then climb up and dig into the scorpion's tail.
The third key is inside a Cage located in an upper alcove in the Egg Snake Chamber. Put the Treasure Scope on and grab a bomb any Kiki throws. Head towards the Egg Snake Chamber and hit the Spring that it is now visible via the Treasure Scope, and place the bomb to destroy the Cage.
Chao Containers locations
Play the Mystic Melody near the Ancient Ruin atop the large central platform in the Snake Altar room. The Warp Hole that appears will transport the player to the first Chao Container's location.
The second Chao Container is in the first green room west of the Egg Snake Chamber.
Break the Wooden Container in the right corner (relative to the entrance) of the room where the Pick Nails were. Doing so will reveal the third Chao Container.
Big the Cat sighting
In the Snake Altar room, climb up to the top of one of the six highest pillars. From there, Big can be seen hanging onto a wall above the room, close to the picture of a flower.
In 2P Battle, there are no Egg Beetles. Both players will start in the Egg Fish Chamber. The room where the Pick Nails would've been in is accessible, and the path between the Egg Scorpion and Egg Snake Chambers is blocked off.
The name of this level is a pun on the word "Head Quarters" which is a term used for a base.
Egg Quarter's and Death Chamber's stage layout are almost the same; this is probably because Death Chamber is Knuckles' version of this stage, albeit, without the robots searching for him.