This Reverse Geocache called the Captain Herrmano’s Mystery Box packs a ton of sensors into the box and some slick programming brings it to like with a full on treasure hunt.
“The housing – that is, the box itself – came from a Nanu Nana store (which is a German chain of stores). Inside of the housing, an Arduino Mega controls and receives information from different sensors and boards – for example a CO sensor (carbon monoxide), a thermometer, an ultrasonic sensor, a GPS receiver, a number pad, a speaker, a display, a mini SD card and a servo.”