Apt (2006)

Across a courtyard, a woman notices lights going out at a particular time and starts connecting what she sees with deaths in the opposite block. A.P.T., also released as Apartment, makes facing windows a deceptively inadequate form of access: you can observe a routine without understanding a life. Ahn Byung-ki leans into supernatural horror and jolting scares, so choose it for an openly haunted version of neighbourly suspicion. The geometry of watching another building gives the ghost-story machinery its useful foothold.