 In level 4 ("Dark Woods of the Serpent"), near the end of the level  you will see a flying carpet, jump to it. It will start flying down  a lava pit. You will see two caverns to your right with a ninja  firing at you. Kill him and jump to the caverns. Behind the caverns  you will find a corridor with some explosive barrels. Shoot them  (from a safe distance). You will now see, through a break in the  wall, a hidden room with someone at the opposite end. Get closer and  you will see that its Lara Croft (from "Tomb Raider") imprisoned.