My wife and I celebrated 20 years of marraige today. We've known each other half our lives now and are looking forward to more years together.
The idea is this: build a box with a latch that is only opened when the box is in a special location as determined by the on-board GPS.
Not being able to leave well enough alone, I made mine with multiple drawers - the first drawer opens easily, but the remaining drawers only open in order at different places around our home town and elsewhere.
The first contained a map and drawing compass, along with a small gift. She's managed to open the next two drawers, but we're nowhere near the final location.
To be continued...