Interstices. The little in-between cracks and crevices of life. This little hiding spot is too small for a pen, so be sure to bring your own.
Cache is hard to find. I rated this as a difficulty 4 for a reason -- I trust the local cachers will let me know if they think that is too high. I had hoped to make this one wheelchair friendly, but I am not confident that it is easily found or retrieved from a wheelchair in the current location, and so I removed the designation. I would be glad to be informed otherwise by a wheelchair geocacher!
Stop and search the corners of your brain for the gaps in your thinking that are preventing you from finding this cache. Maybe a thought will poke through an opening giving you an idea of where to look. Maybe there is a fissure with an idea in it. You may be glad for a cache extraction tool... once you find it. Happy hunting.