Yiannis. I’ve been lucky enough to get to quite a few very good dark-sky sites around the world. I have been to the Spaceobs site in the Atacama a couple of times, San Pedro de Atacama is one of my favourite places and the skies at Spaceobs are the best I have ever seen. It is a long slog to get there from the UK but definitely worth it. If you go in the southern hemisphere winter you get the centre of the galaxy overhead which just adds to the majesty of the sky.
This is a stacked set of 10s exposures with a 50mm lens from Spaceobs: https://www.flickr.com/photos/nickdjames/48273525482/in/album-72157709616722002/
There is a wide selection of telescopes to use too: https://www.flickr.com/photos/nickdjames/48273530247/in/album-72157709616722002/
La Palma is a very good choice for dark skies too and a lot easier to get to!
Your images from Sikinos are very good. A good excuse to spend a few days on Santorini too.