Well, I visited some places.
Not dedicated to astronomy, but very dark sky (Bortle 1-3):
South Africa:
https://www.olivegrove.co.za, 20km south of Beaufort West
http://leeuwenboschfontein.co.za very dark twice a year star parties are held there :
https://southernstarparty.org
Several accomodations in Sutherland (close to the observatory which you can visit)
Australia: Various nice and dark places.