I've never been to Tsarskoye/Pushkin, so this is just a guess based on instructions, photos, and images from Google maps...
Step one: AP to Akademicheski Prospekt

Step two: Akademichesky Prospekt to ruins

Again, this is a guess. The building I've circled seems to match the size, shape, placement and color of the train station when seen via Google satellite images. When I zoom in, it's also the one of the few unlabeled building in the vicinity, which makes me think it could be the ruin. Please correct me if I'm wrong.