I've been wanting to set a story in an indoor pool for a long time. To me, indoor pools are very sinisters places. They look strange: the wavering water casts shadows on the tiled walls. They smell strange: all that chlorine can't escape like it does outside. They feel strange: slimey and rough at the same time. They sound strange: sounds seems to bounce off every surface. They taste strange: the chemicals and humidity choke me.
But maybe indoors pools wouldn't freak you out in a story at all. Maybe you grew up on them and it's fruit cellars or animals dressed like humans that scares you.
What motiff or setting do you want to use because it's scary or sinister to you?