The Jewel of the Nile is DLC for Serious Sam 3. It is available for the PC, Linux, Mac and Xbox 360 versions of the game. It costs $9.99 USD on PC, Linux, and Mac. It costs $2.49 USD for Xbox Live Gold members, and $9.99 for non-Gold members.
The Jewel of the Nile contains three new single player levels, a new weapon, new enemy and a new boss. Game play is similar to the base game, but there's more of an emphasis on using weapons such as the RAPTOR Sniper Rifle this time around. Levels are mostly as linear as the ones in the default game, but there's one spot where the player can choose to do four puzzles in whatever order they like. There's also a part where the player can use the Jetpack, which marks the first time it can be used outside of a boss fight.
In addition to three new levels, the DLC also adds a new weapon, the Axe. It is basically the same as the Sledgehammer. The Aludran Reptiloid also makes a return, along with a new boss. The RAPTOR Sniper Rifle and XL2 Lasergun are now regular weapons, instead of being hidden in secrets.
The Jewel of the Nile takes place after The Power of the Underworld. After activating both of the Sirian power generators for the Time-Lock, Sam and Wilson head back to headquaters. However, along the way, Quinn tells Sam that the Time-Lock is still not up and that he needs to go to the Island of Philae in order to find clues on how to activate it. After some protesting, he does so.
On the Island of Philae, Sam finds a statue of the Goddess Isis, then puts it on a pedestal. This activates a system that eventually lets him open a door hidden in a tomb. Past this door is a keycard, a holographic map that has information that shows where the Time-Lock's control room is, and obtain an XL2 Lasergun. Sam takes the gun and the keycard then heads to Abu Simel.
At Abu Simel, Sam finds himself near the Tomb of Ramses, but is unable to get there because there is a gate. He heads to a nearby abandoned military base, grabs some C-4 Demolition Charges, and blows the place up. After some fighting, Sam finds himself inside the tomb, but only finds a statue with a spot for another. After talking to Quinn for a bit, he learns that there should be another statue that'll fit on the spot, but she doesn't know where it is.
Sam then enters a nearby temple in order to search for the missing statue. In the back of the tomb, there is what appears to be a door, but there's no way to open it. After exploring for a bit, his Sirian Mutilator makes two statues move, each revealing a switch. After using each switch, four statues in the back of the tomb move, revealing hidden rooms. Each room has a puzzle with a switch at the end.
After using all of the switches, the area beyond the door in the back of the tomb is finally open. Sam then finds the missing statue, and places it next to the statue he found in the Tomb of Ramses. After doing that, a door opens, revealing another Sirian chamber. Inside it, Sam does not find the Time-Lock control room, but instead finds a seal that will open a door to the tomb of Sethirkopshef, which is nearby. Sam then heads off to go to the tomb.
When he gets back outside, Sam finds himself near a Dam he needs to cross. However, there's no way to get over it. With some exploring, he finds a Jetpack in a nearby abandoned depot, and uses it to fly over the dam. Soon afterwards, he finds an entrance to a pipe, but it's also locked. After fighting some enemies, Sam finds it in a storage room used for the dam. Sam opens the pipe and enters it. Unfortunately, he is thrown into water, which short circuits the Jetpack. Despite this, Sam moves forward.
At the end of a grassy path, Sam finds the tomb of Sethirkopshef. However, it is guarded by enemies and needs a keycard to open a gate that leads to it. After clearing out the enemies and finding the keycard, Sam enters the tomb and uses the seal he found earlier to open a Sirian door. Past the door is the Time-Lock control room. After fiddling with it for a second, Sam manages to activate the Time-Lock. He then learns that a helicopter will be coming to pick him up, so he heads outside. However, he finds a huge Scrapjack armed with powerful weapons waiting for him outside.
Despite the odds, Sam manages to kill the beast, and is then picked up by Wilson, which ends the DLC.