The cache is located at the specified coordinates. In order to open it, you have to complete the following caches first:

Musikalische Ge(o)heimnisse: Bermudadreieck

Musikalische Ge(o)heimnisse: Musikbibliothek

Musikalische Ge(o)heimnisse: Der Mai ist gekommen

You will find a bonus word in each of them - the first letter must be converted into a number.

Those three digits in the order listed above will open the lock!

This cache lets you trade music. The initial swag comes entirely from artists and bands from Hannover. Would be nice if that could be respected as a criteria for your trades.