Halls of Demetrius

Run down the stairs to come to the halls of Demetrius. Run up the stairs on the right. Pick the Pharos Knot from the pedestal. Get back down into the hall. Now run up the stairs on the left. (Movie: Lara will read a scroll. Werner and three of his killers will arrive. Lara will flee and so will Werner.) You are back in the hall. Shoot the three baddies coming down the stairs. Now run up the stairs. On the left side, you'll find a lantern. Pull it along the markings. The door, where Werner disappeared, opens. Step through. Follow the path.

Coastal Ruins

You'll return to the coastal ruins. Slide down to land in the pool. This will automatically trigger Secret 53. Climb out of the pool. Now climb onto the platform in the middle and collect the Broken Glasses. A couple of times people have asked me what the glasses are good for. There is no use for them. I suppose it's a sign saying, "you are on the right path". Climb up the ladder in the shaft. Run up the stairs and step outside. Drop down to the left. Jump into the water. Dive towards the left.

Passage to Isis

You now have to take the path on the right (see image) but to collect some goodies continue to the left. Now take a deep breath and dive into the passage opposite the ruins. Dive into the big chamber. Dive into the passage on the left where the seaweed is. The current will take you to the next level.