This is a spoiler guide to show you how to get the 2 milestones in the Saharaland Update.
How to Get Secret Milestones
The Skullcat Sphinx
The secrets of the sphinx
Press the Hidden Button on the Left side of the Sphinx to open its Treasures!
Unlocks: Skullcat Scepter
Trials of Skullcat
Then move upward to the Great Pyramid, and follow the map to get to the Hidden Lab!