A small crack
An unfamiliar castle can look threatening. A familiar path needs less scenery: a door that was not open yesterday, a sound in the wrong place, an explanation that does not match a memory.
The place remains almost the same. That almost creates tension. We recognise the world while becoming less certain that we can trust it.
Landscape as memory
In the worlds of Horror Oberpfalz and Der See vergisst nicht, landscapes carry traces of things people would rather leave behind. Forest, stone and water do more than provide a backdrop. They give what has been suppressed a place.
A question emerges: what happens when someone looks more closely? A character can turn away, investigate or become involved. That decision turns an unsettling observation into a story.
Reading what is unseen
A story need not resolve every uncertainty at once. If a sound has two explanations, readers have room to fill in the gap. A later clue may change that space.
On your next reading, notice when a place stops feeling reliable. What has the text actually shown? What have you added yourself? Perhaps the strongest shiver lies somewhere between the two.