ShotHotspot has mapped 12 abandoned places in Kowloon, Kowloon City, ranked by how often they're photographed, viewed and voted for. The most popular are Ma Liu Shui Ferry Pier, Ruins Stone Loading Ramps and Abandoned Kwun Tong 再見裕民坊. Some are private property or unsafe, so get permission before you visit.
We don't know whether you're allowed to visit any of these places. Many are private property, closed to the public or unsafe: get permission from the owner or the relevant authority, and take safety precautions.