This is stage 2-5, the fifth level in the Migen's Shrine region.
Clancers who are swinging in the cavern tell Marina that she can use them as rope to get across the lava. However, they warn her that she shouldn't stay hung for so long as the Clancer won't be capable to support the weight and it'll fall on lava along all the Clancers that are below it.
Grab the swinging Clancers to reach the Level Completion Stars.
When you get to the end of the level, keep going right on the clanswings and you will come to the golden gem sitting on an island surrounded by red and blue gems.