The phrase "unforgettable wonder" is not a normal English phrase. It would sound strange to use in conversation or in almost any context. However, it does make sense.
"Unforgettable wonder" would refer to something positive and amazing. For instance, if money started falling from the sky, it would be an "unforgettable wonder." It would refer to something so fantastic that it's not even possible. You would only use the phrase "incredible wonder" as hyperbole, not in everyday speech.