Geocaching is a popular hobby around the world. This code is used for a cache nearby my house. It's easy to find, but difficult to open: you have to show some morse code skills before you can access the logbook!
More details can be found on this blog post on my website: https://www.pa3hcm.nl/?p=1769
For more information on geocaching please visit this website: http://www.geocaching.com/