After dropping the crystals you will have to solve a little puzzle again... After solving it (should start snowing now) you'll have to get to "Pinguin Insel" (should be marked on the map after talking to one of the traders).
(just 'use' a penguin and get right back to the oldest in MV then)

Circle of stones? In a cave...? The pirate's cave... (which is darkened)?

(also hoping my english isn't as bad at all )

Yeah, it snows thanks, but none of the traders said me where is the Island... And the strange thing - one of the traders regularly disapears.

Sorry, I mean a "stone circle" (this on the wall in a pirate's cave) Red text appears when I go near it.