This is a Challenge cache; in order to claim the
you will need to find 25 Virtual or Ghost caches
A Virtual Cache is about discovering a location rather than a container. The requirements for logging a Virtual Cache vary—you may be required to answer a question about the location, take a picture, complete a task, etc. In any case, you must visit the coordinates before you can post your log.
Although many locations are interesting, a Virtual Cache should be out of the ordinary enough to warrant logging a visit.
I have to be honest, these are among my favorite type of geocaches, they take you to amazing historical places, full of unique and interesting views. It is a bit sad that geocaching decided to grandfather them; therefore the few we still got left around the world are priceless.
You can check your answers for this puzzle on GeoChecker.com.