Hop over the window and pass through the sawblades (use the Eye of the Storm if you need to) and head for the dead end. Run up the wall and use the Stab square and jump up to the top BUT BE CAREFUL! There are two Archers standing guard!

When the coast is clear, use Quick Kills on both Archers and then move forward to trigger a cutscene. After the cutscene, access the Water Fountain.

Save point