There is an old superstition that people have an easier time seeing spirits through a keyhole, knot in wood (like in a fence) or a hag stone (stone with a hole naturally eroded in the middle). If you look back at many fairy tales, legends, folk tales and old personal accounts, keyholes and other small holes tend to surround many sightings of spiritual things. I once read an account here of a women who looked through her fence and saw another woman in an old fashioned wedding dress being prepared by another women. When she looked over the fence, they were gone.
The psychology in this is that by peering through something, it is looking in a different way, therefore we are more open to seeing what is normally unseen. Spiritually, it is believed that they are tiny portals we can look through. I've personally been searching for a hag stone my entire life. It's something that has always interested me since I was a child. I've never come across one, but I continue to keep my eyes open. They're supposed to be naturally made, not artificially drilled.
So try meditating and afterward, take a look through one of the things I've explained. But don't give up, just because you don't see something, doesn't mean it won't work. Perhaps there is nothing to be seen just yet.