This cache is hidden less than 200ft from where the NDB used to stand. The cache is hidden on private property with owner permission.
An NDB is a radio based navigational aid (navaid) that was once widely used for navigation. The concept behind its operation is incredibly simple. A pilot tunes an NDB's frequency into one of their navigational radios, causing the needle on their ADF (Automatic Direction Finder) to point towards the NDB. It doesn’t directly tell the pilot their distance to it, but it does allow them to have a general idea of their location.
NDBs were one of the first navaids available to pilots starting back in the 1940's. Since then, navigation systems have improved, starting with VORs (Very high frequency Omni-directional Range,) DME (distance measuring equipment,) and, most recently, GPS. Since GPS was introduced, the FAA has been considering a phase out of NDBs and VORs, yet it is highly unlikely that will happen for the foreseeable future. These are still relevant navaids that still have some use, yet the majority of pilots never learn to use them (because they learn GPS with VORs as a backup.)
I assure you, the cache is easier to find than it is to understand the previous two paragraphs.