New content has just been added to the Overworld area in Lara Croft and the Temple of Osiris. If you follow the path to the southeast of the central Shrine of Osiris, where there used to be a broken bridge overlooking a deep ravine, that bridge now connects to a new explorable area: the Sunken Chapel of Sobek.
The Steam version was slightly delayed, but this new area is now available for all players. It includes more red skulls and health/ammo powerups to collect. For those who purchase the Season Pass, the Sunken City will eventually allow access to new DLC tombs—the Tomb of Hoarfrost and Tomb of the Embalmer—when they are released. Dates for these have not yet been announced.
The new Community Challenge feature rewards players for working together. If you want to get your hands on special items like gold weapons, bonus bags of gems, and a few surprises, check out the Community section in the game's main menu. Each week a new challenge will be posted. This week's challenge, "Burn Baby Burn," requires that everyone work together to kill 5,000 exploding, flaming mummies using SMGs. This particular goal has already been met, so everyone can now go to the Community Chest in the Overworld to find those special weapons waiting. (This is the treasure chest at the edge of the shrine to Osiris, where DLC items appear. It's shown in the screenshot below.)
Note that community challenges are run separately on each platform. That is everyone gets the same weekly challenge, but Steam, PS4, and Xbox One players will work with other players on that same platform. Challenges will run from Sunday (12:01 AM PM PST) to Saturday (11:59 PM PST) each week. The reward will be available in the Community Chest as soon as it is unlocked, but will only remain for 24 hours (11:59 Sunday night) after the challenge closes.
Visit this thread on the Square Enix forums for a detailed list of Lara Croft and the Temple of Osiris patches, including the Sunken City update, as well as various crucial bug fixes for all three systems. Check this thread for Community Challenges.