Ghosts in stories tend to represent a single person – a child who died young or was killed, whose presence continues to haunt her family, the victims of a serial killer who haunt a house, a woman killed on a highway who scares passing drivers. For me, a non-believer in ghosts, I see these as metaphors – a past horror can haunt your mind long after it happened. In this exercise, lets play with the idea of ghosts as a memory we can’t get away from, but instead, lets have those ghosts represent events or ideas rather than a single person. So maybe in your story the protagonist (a single person, or a whole community or country) is haunted by slavery, or the hospitalisation of people due to their sexuality, the invasion of a country, or a hurricane and flooding where people were left to drown, rather than helped by the government. The past continues on, in certain ways, into the present – and in that sense, we might say it haunts us still.
Pick a past event, situation, idea, or social injustice that you still feel vibrating in the present, and describe how it haunts your people still (using poetry, story, or just an isolate description – whatever appeals to you). You can focus on the event, personified as a ghost and being active in the story (ie what characteristics would slavery as a ghost have, how would it act?), or you can focus more on the consequences and the way this event effects the present (what evidence is there of harsh discrimination against sexual diversity today? – not to suggest that it doesn’t continue on today, but rather how do we sense some past injustice in the bones of buildings, in the way we talk…).