The Overworld is the Hub Level in Lara Croft and the Temple of Osiris. It is divided into several locations:
Shrine of Osiris
The Shrine of Osiris is the main hub. It is more or less in the center of the map and contains the shrine where Osiris is being reassembled as well as the small chamber where the time of day and the seasons can be manipulated. All other sections can be accessed from here.
Osiris Shrine Interior
Osiris Shrine Interior is the small chamber under Osiris's Shrine that controlles the seasons and the time of day (nighttime or daytime).
Temple of Osiris
The Temple of Osiris is where the characters leave the pyramid for the first time in the beginning of the game.
The Khepri Amphitheater is a huge structure where fights to the death are performed.
Waterfall of Sobek
You have to get past the waterwheel to get to the Waterfall of Sobek.
The Cliffside is at first only available in winter as you have to get across the frozen river.
Sunken Chapel of Sobek
The Sunken Chapel of Sobek appeared with Patch 1.2 and contains the Downloadable Content: