SECOND ALTERNATE ROUTE TO LOST LIBRARY AND HALL OF DEMETRIUS:

If you didn't open gates C or B in the COASTAL RUINS, you'll need to take a different route to get back to the LOST LIBRARY and/or HALL OF DEMETRIUS.

After sliding back into the COASTAL RUINS from PHAROS, TEMPLE OF ISIS (through the chute marked G on the map of the ruins), climb out of the water on the right (west) side of the pool. Follow the rocks toward the building with the ramp and climb up on the left, opposite the ramp.

Go over or around the dunes toward the building to the southwest.

Enter the building here. (This is the door marked D on the map of the ruins.)

Climb the stairs and jump to grab the edge of the ledge with the pulley underneath. Pull up.

Move around to the second jutting ledge and take a running jump over to the ledge with the pointed archway.

Go through the open gate to get back to the CATACOMBS.

Go straight through the first room to the smaller room with the climbing pole.

Slide down the pole.

This brings you back to the high ledge at the east end of the HUGE ROOM WITH HIGH PLATFORM, ROPES, AND SMALL POOL. Take a running jump to grab the ladder on the north wall and climb down to the floor.

Head for the west end of this large room and go through the doorway next to the shallow pool to re-enter the TEMPLE OF POSEIDON.

At the top of the stairs, climb down the ladder opposite the alcove with the golden bird statue to reach the JUNCTION below.

This is the area where you activated the 4 POSEIDON SATUES earlier, diverting water into the deep pit. Dive into the flooded pit.

Swim down through the passage on the west wall...

...then through the narrow opening at the bottom of that passage on the left.

This leads to a room where you can climb out of the water. Follow the stairs up to the left.

This leads to the ROOM WITH FOUR SMALL POOLS, where you found the LEFT GAUNTLET of the ARMOR OF HORUS earlier.

Go through either of the small doors flanking the sarcophagus.

Follow the passageway around the next corner. There's a raised crawlspace about halfway along the passageway on the west side. Climb into it.

Crawl through, and continue to the LOST LIBRARY.

If you have not yet completed the LOST LIBRARY and HALL OF DEMETRIUS, follow the LOST LIBRARY walkthrough from the beginning to get the PHAROS PILLAR. Then continue to the next level, HALL OF DEMETRIUS to get the PHAROS KNOT.

If you have completed the LOST LIBRARY and HALL OF DEMETRIUS but missed the PHAROS PILLAR, check the section near the end of the LOST LIBRARY walkthrough on returning to the upper level in order to find the artifact. Then retrace the route shown above to return through the crawlspace back to the TEMPLE OF POSEIDON. Follow the POSEIDON walkthrough to open gate C and return to the COASTAL RUINS.

If you have completed the LOST LIBRARY and HALL OF DEMETRIUS but missed the PHAROS KNOT, go through the big doors at the east end of the main hall in the the LOST LIBRARY (shown in the screenshot above) to re-enter the HALL OF DEMETRIUS. Follow the DEMETRIUS walkthrough to find the artifact and exit back to the COASTAL RUINS.

Once you have both artifacts, re-enter PHAROS TEMPLE OF ISIS through the underwater passageway at F on the map of the ruins.

[Pharos Walkthrough]