The easiest way is to finish the level, then you are back at the pond with the Golem.
You then can go back into the beginning of Hyaku Lake and search for the 2nd rune.
If you can't find it go to www.pcgameswalkthroughs.nl
, to the English section and there you find a English text walkthrough with lots of screenshots.
After you have found the rune you have to play the level to the end to go back to the pond with the Golem.
Maybe you don't have to solve the Lake puzzle again because they are already solved, when you are at the lake go down to the pond.
Make it freeze and if you are lucky you can go to the last part of the level to the teleporting disc.
Succes and have fun