[Stacey42]

My favorite difficult one was at a roadside park. Someone had gone under a wooden picnic table, & found a hole in the wood, glued a tiny magnet in it and then put a tiny metal container in the hole, with just the smallest bit of a metal curve barely visible. You had to get pretty much under the cobwebbed table and run your fingers over it to tell that it moved and then I had to get DH's multi tool to pull it out.

We found another one done like it in an old wooden sign with a small piece of wood, protruding ever so slightly to let you know something might be there.

My favorite clever ones locally are the ones disguised to look like solid metal outlet plates or random bits of plumbing/electrical work that don't really belong. There are two cache teams in our area that are really good at disguising things that way and you have sit there and ask yourself 'what is wrong with this picture' when you know you are at ground zero. My kids have taken to just pulling & pushing on anything that doesn't look like an actual electrical outlet when it's one of these guys' hides.

I really suck at the puzzle ones that give you coordinates to the first part of the puzzle but then you have to figure new coordinates out from there.