Create a reflective experience engaging the 5 senses to evoke different memories within different visitors.
Because involuntary memories often occur when people daydream, relax, or are unfocused, it could be necessary to give them a space where they feel comfortable enough to sit and be still for awhile.
Providing some sort of sensory stimulus can help direct their thoughts but still allow them to be involuntary. It also gives a reason for them to sit, engage with the space, and let their mind wander. This could be through sounds, images, possibly touch and scents, and written stories describing a sensory experience. Journals could be provided for them to write their experience in if they wish.