I saw this movie on DVD sometime between 2012-2016, but the movie itself could have been older. It was in color and was live action. Two kids used a hang glider to travel through a (cloud, fog, storm?) portal, which got them on an island (not sandy, but grassy, reminds me of the Scottish highlands, also near a bigger price of land) that had a bunch of nuns on it. The building was very castle-esqe and stony. That’s pretty much all I remember, but I know it wasn’t a horror movie.