hauntingly
In a way that sticks in your mind and feelings.
Hauntingly describes something so beautiful, sad, or strange that it stays with you long after you experience it, like a memory you can't shake. A hauntingly beautiful melody might echo in your mind hours after the concert ends. A hauntingly sad story lingers in your thoughts for days.
Just as a ghost supposedly haunts a house by returning again and again, something hauntingly memorable keeps returning to your thoughts. You might describe a photograph as hauntingly beautiful if its image keeps appearing in your mind's eye, or call someone's voice hauntingly familiar if it reminds you of something you can't quite place.
When writers use this word, they're usually describing something with emotional power: a hauntingly empty playground, a hauntingly lovely painting, a hauntingly mysterious smile. The word suggests that what you've experienced has gotten under your skin in a way that's hard to explain but impossible to ignore.