The "Mountain" icon What it means

[Gnarl]

Sometimes I do inspect and there's a moutain type icon over a building. What does it mean? I feel I'm missing some item or follower at some of these spots but can't figure it out or might have missed a message saying what to do.

Thanks in advance.

[Perish_Song]

Its a story location to enter. Either you've already visited it, or you will be accessing it later.

[kef34]

you can take a selfie in front of it where you stay on the side instead of the middle of the picture. that's about it