Now take the wide stairs (towards the bottom of the screen) and proceed to the exit - take the closed gate (it's the one opposite to the path leading to Ti Kah's daughter's house). Take the next gate (on the right) and march to the left, along the brick building.
When you reach the place where a gap in the fence is visible (top of the screen), turn into the path between the lampposts - it will lead you to another building, with the door embellished with golden ornaments. Enter these doors.
You will find yourself in a swimming pool. Go left and take the ladder (around the middle of the pool) and get to the bottom of the pool.
Proceed to the right and notice the interesting mosaic at the end of the pool - pay particular attention to the colors of the stones there (2 blue on top, 2 green in the middle - a red one in-between them - and 2 blue at the bottom). Go back to the ladder and climb back up - proceed left.
Now take the stairs leading to the higher diving platform (straight across the entrance door) and get to the top. Go through the end of the end of the platform and zoom in. Install the three lenses in the holes. The blue on to the left, the green one in the middle, and the red one on the right. Click twice on the active point at the end of the platform that Kate is standing on.
Direct the lens rays to the right stones
You will now switch to a top-down view and see the lenses that have came out of the pool's bottom. Some of them can be turned in zoom (spyglass icon), thus changing the angle of the rays. The other ones can be turned from the top (gear icon). The task is to lead the rays to the corresponding stones on the door. The red ray has to land in the bottom. On both sides of it, you want to have green rays. As concerns the blue ones, two have to be at the top, and two at the bottom.
The easiest way of getting about this is by beginning with the red ray. You want the red ray to go as shown above.
In order to do that click on the lens marked in the picture by letter A and while zooming in (by moving your mouse to the right) aim the red ray at the lens no. 1 and then zoom out. Now you only need to aim, while zooming in, the ray from the lens no. 2 (by moving your mouse to the right) at the red stone in the center of the temple's gate (3) and then zoom out.
Then the green ones. Refer to the photo above. For the sake of clarity, we're showing only the path of the green rays - you might as well begin with them.
Click on the ray marked in the picture by letter B and, while zooming in (by moving your mouse to the left), aim the green ray at the lens no. 4 (and then zoom out). Now, you must aim the two rays that comes out from the lens no. 5 in a such way (by moving your mouse to the right) that one of them is reflected by the lens no. 6 and the second ray by no. 7. Finally, while zooming in, you must aim the ray from lens no. 8 (by moving your mouse to the left) at the green stone on the right of the temple's gate (9; right from the red one) and the ray from lens no. 10 (by moving your mouse to the right) to the left green stone on the temple's gate (11; left from the red one).
Then the blue ones. The path of the blue ras should look like on the above picture. (Again, for clarity, we're showing only the blue ray here, but mind you that the green ray has to be set first, otherwise the blue one will be disrupted when setting up the green one). As you can see, the green ray had to be moved a bit in order to give a full exposition to the blue one.
Click on the lens marked in the picture by letter C and while you are zooming in (by moving your mouse to the left) aim the blue ray at lens no. 12 (then you must zoom out). Next, the two rays that comes out from that lens must be send to (by moving your mouse to the right) - one to the lens no. 13 and the second one to no. 14. Two rays from lens no. 15 must be aimed at (by moving your mouse to the left) - lens no. 16 and the second one at no. 17. When they deflect them off they will automatically hit the two blue stones on the temple's gate. Then, while zooming in, you must send the ray from the lens no. 18 (by moving your mouse to the right) to no. 19 (and then zoom out). From that lens you must send two rays (by moving your mouse to the right) - one to the lens no. 20 and the second to no. 21. Now, while zooming in, the ray from the lens no. 20 must be send (by moving your mouse to the right) to the blue stone in the lower right part of the temple's gate (22) and the ray from the lens no. 21 must be send (by moving your mouse to the right) to the left stone in the lower left part of the gate (23).
(If you manage to figure out this configuration in less than 20 moves, you will get the Raiders of the lost temple achievement).
When the gate opens, go down from the platform and towards the bottom of the screen, then left. Get to the bottom of the pool using the ladder. Go through the door (achievement: O spirits, are you there?).