One of my caches (made from a piece of central vac tubing) - it has a bit of bubble wrap for the inside bottom, a larger 'pill bottle' for the cache container that contains a log book and small items, and a piece of #10 gauge copper wire) ... to get the cache out the finder must use the copper wire and push it through one of the holes on the bottom to bring the cache container up to the top. I called this cache (sunk'n) ... the cache is mounted about 4' high, so the holes on the bottom are not obvious. The bubble wrap is a cushion for the cache being dropped back into the container.
The top is to keep rain/snow out and has been chained to the fence (so it doesn't get lost) and sanded inside so it slips off easily