This is the overworld map of Serious Sam: The First Encounter.
You start your adventure at Hatshepsut Temple at the bottom of the map, and make your way to The Great Pyramid at the top.
The Moon Mountains and the Sacred Yards are optional and secret areas.
Hello how can I unlock the Mountains of the Moon and the Sacred Yards
It’s been way too long, but I believe that there was a secret entrance from the end of the level before each of them. I suggest finding the details in an online walkthrough, as I can’t remember after all these years.
For moon mountains you need to destroy by rocket big rock from up-right when you entrance cave with water at the end of “valley of the kings” map. It activates pendulum bridge. You need to use it to reach another edge of cave lake and go to secret level