Near the top of Mt Psiloritis, at 1750m, Skinakas Observatory is operated by the University of Crete and is the country's most significant stargazing vantage point, with two powerful telescopes. From May to September the site opens to the public once a month around the full moon (see the website for exact dates). There are presentations and a chance to look through the telescope.
Note that the road here is in poor condition, and often not passable if there's snow on the mountain.