Here, you have to get 5 gems and bring them to the guardian – that big bluish/purplish rock.
First get the 4 gems in water:
1, down in the hole
2, get sonar and blow the rocks away
3, beside that jump over
4, in one of the houses
Then get the rings that appear in the air, and go into the main building to sonar the Roundy things that appeared.
The rings are now activated. Go through them starting the lowest one, and if you give yourself a boost at the beginning, then swim fast, you should get the 5th gem up in the air.
This is the end of Isle of Tranquility, which means you start Man’s nightmare without all your extra health collected with the vitalit crystals.
