.. Getting to the yellow tuning key

You can save the game now so you can easily load to the moment you are pased the boulder.

Next, by going through the boulders try to get to the ponds.

The upper pond will make you light. When you are light you can walk across the bridge.

The effect will wear off, yes. You have to find the quickest way. The pond that makes Cisco strong is not part of the solution.

You can also move backwards the portals. So, return to the portal you came from.