Dear Zesty, Elodea is indeed a vast universe to explore consisting of four worlds, Elodea mainland, Elodea Unterwelt, Elodea Tunnelgang and Elodea Schatzkammern ...
I don't know how far you've been making yourself familiar with its environments and requirements to proceed ... So, at first there are seven cloths to be found in each of those worlds to find and open a special 'key room' offering more clues to proceed ... you also, after having found all of the 7 cloths, are then able to find the resp. linking book to the next world, in your case Elodea Unterwelt ... this means at your point (with 7 cloths clicked) be vigilant to search the island for 'a path' to that book wherefore you have to search for hotspots everywhere to activate sth (this is already a hint) ...
Where you are at right now, I suppose and I hope I got that right, is, where you have to go back up the way you've been 'going up' already in the beginning to arrive on Elodea's mainland ... It is atm unfortunately not possible to directly link back to where we've been leaving the world, means we always have to go back to the main island and through the found passageways/books and this also applies to proceed again to the next worlds of Elodea, but as there is a special link on the mainland besides the 'next for Unterwelt', maybe you've seen it already, to another Elodea world it will not be too arduous to continue on a more advanced level of progression into this universe ...
This sun ornament in general is transporting you back to the last cloth you've been touching btw, just like the cloth in our Relto linking books, so maybe you've found all seven cloths already, but that's my speculation right now ... However, now you know how to get back to the island and I'd recommend you read through the following thread with many hints and tips about and for proceeding through Elodea successfully,
just start with the second page right here ... Zesty, I hope that I put everything right and understandable for you and wish you an exciting journey through that awesome and wondrous universe, it is worth every effort ...