Μ
A series of caches based on the letters of the Greek Alphabet. There are 24 letters in the Greek alphabet. They've been around since around 850BC. The Greek alphabet is itself derived from the Phoenician alphabet. The Greek alphabet has itself been the basis of other alphabets including the Latin alphabet.
Modern Greek letters today, are used for symbols in mathematics and science. amongst other things.
"Mu" is the 12th letter of the Greek alphabet. It is derived from the Egyptian hieroglyph for water. Mu in its uppercase for is not used as it's too near "M". In it lowercase form μ, in engineering it represents the coefficient of friction. In music it is a major cord. .
The cache is a small lock and lock box placed at ground level.
You will need to bring your own writing implement