This page explains how to find the Sheh Rata shrine and solve the "Speed of Light" puzzle.
How to Reach the Shrine
Before you go to the shrine, sure to have some way to make fire, such as fire arrows or some flint (from breaking ore deposits) and bundles of wood.
Go to Mirro Shaz Shrine or Woodland Tower, then go south on the nearby road. Look for a bridge to the right, and go across it. On the other side, go south along the river. When you see the shrine, go toward it down to the beach. There is a thin sand bar under the water that you can walk along to reach the shrine (the map shows it if you have activated the tower).
The shrine itself is surrounded by thorns. You have to burn them to get rid of them, so either shoot a fire arrow at them if you have one, or put a piece of flint and a bundle of wood on the ground, and hit the flint with a metal weapon to set the wood on fire.
After the thorns burn away, you can enter the shrine.
How to Solve the Shrine
There is a chest on a ledge just below where you entered the shrine. It contains an Opal.
Rotate the wheel near where you entered the room. This will rotate the platform with a laser on it. The laser will eventually hit the crystal switch, raising the water level.
With the water level raised, use Cryonis to go to the crystal switch. Put a remote bomb next to the switch, but don't detonate it yet. Instead, go back to the wheel, destroy any Cryonis platforms that might be blocking the path between the laser and the crystal switch, and rotate the wheel. Before laser activates the crystal switch, quickly swim to the far area of the room, where there is a metal barrel and underwater switch.
After the water level is lowered, put the metal barrel on the switch, then go through the gate that opened, but don't talk to Sheh Rata yet. Instead, detonate the remote bomb to raise the water level again. When it is raised, use Cryonis on the water beside the treasure chest ledge. Climb up and open the chest to get a Giant Boomerang.
Then talk to Sheh Rata to get the Spirit Orb.