Apart from the debatable idea that some places have inherent weirdness (be that deriving from electromagnetics, pressure changes, leylines, 'sacredness', whatever) -
would you think that the physical process of getting to many tma-ish places is the kind of thing that might induce a meditative state of brain/mind? All that physical exertion to get up the hill. Rhythmical movement of your arms and legs. (In my case) heaving lungs and lack of oxygen to the brain. Plus the fact you often get enveloped in the noise of the wind (not really white noise? something like it anyway) which is kind of sensory deprivation.
Thus your state of mind might be particularly primed to experience things that would normally be too far off the edges of your perception??