Once you've dealt with the huge creature, you will be rewarded with a short cut-scene (#1). As you've probably noticed, the body is now located near the exit. You will have to swim there. Once you've reached your destination, head on to the nearby rocks. You should be able to reach the dead body from here. Start running towards the upper corridor (#2). You will have to make a single jump along the way.
Keep moving forward. Once you've reached a large gap (#1), make a double jump in order to use the grapple. Thanks to that, you will be able to reach the opposite end of this corridor safely. There's a metal post here. Use it. Now you will have to reach a large slipway. Be careful, though. You will have to make a jump in a few seconds (#2).
An interactive cut-scene will appear on your screen in just a few seconds. Lara is going to be attacked by a second creature (#1). You will have to avoid its attacks. Thankfully, there's not much to do here. You will only have to press a few movements keys. Once you're in a new corridor, start off by entering the Accurate Aim mode. You will have to start shooting at the highlighted object (#2).
In order to leave this room, you will have to use a narrow ledge (#1). Make a jump towards the upper platform. There's a rope nearby. Use it. Thanks to that, you should be able to reach the next gate. Pull a large lever in order to open it (#2).
Get down to the lower level. There are enemy soldiers in the next corridor. You will have to take care of them. I'd personally recommend using a nearby lever (#1). Thanks to that, you won't have to shoot them yourself. Use the lever again in order to get rid of the flames. Proceed to the next room. There are a lot of enemy units nearby (#2). Most of the soldiers will be standing on an upper balcony. You must kill them quickly. Be careful, though. They will be throwing a lot of grenades at you!
You won't have to visit the upper balcony. Instead, start moving towards the next corridor. Be careful! One of the soldiers will surprise you near the right gate (#1). Kill him. Now you will have to reach the opposite end of this corridor. Once again, it'll require you to avoid traps. You might want to consider making single jumps, although this is quite risky.
You'll meet some additional enemy units along the way. I would recommend doing a lot of slides (press the F key while running). Thanks to that, you should be able to take out an opponent for a few seconds. Once again, you will have to avoid a mysterious substance (#1). Make a jump towards the opposite ledge. Once you've reached the main hall, take care of the remaining enemy soldiers. Now you will have to make a jump towards the small elevator. Press the button (#2) in order to start moving upwards.
Be careful! You will encounter additional enemy units at the top (#1)! It would be wise to take care of them quickly. Make a jump towards the nearby stairs. You may proceed to the well known corridor. You will be attacked by a large group of enemy units. Start off by taking out two nasty dogs (#2), mostly because they pose a serious threat.
Keep pushing forward. The last group of enemy soldiers will be waiting for you inside a large warehouse (#1). It's the same spot where you took the fork lift truck. Once they're gone, a long cut-scene will appear on your screen (#2). You will find out more about Lara's current plans. This time she decides to take a trip to Nepal.