This is the first manga I've read by this author, after hearing about him on youtube. I feel like the premise is really interesting, but in execution it comes off as a bit... abrupt?
Still makes no sense that noone smaller could enter a hole made for a bigger person. Or that the hole also takes the hairstyle of the person into account.
as they(she?) said, the hole is an exact silhouette of you, a silhouette is just your picture with one single fill usually black, which here symbolically, is replaced with the darkness of the mountains which consumes you to make the silhouette(hole0 'whole'.