The phrase "unbelievable experience" means something that is hard to believe or very difficult to comprehend because it is so extraordinary or amazing. Full definition
It will probably be amongst one of the most wonderful and unbelievable experiences in my lifetime. (biofieldhealing.com)
This is the most unbelievable experience I have ever had with a bank. (ptmoney.com)
We are very proud of the fact that we have numerous members that have remained with us since the early 1980s, and continue to log in unbelievable experiences year after year. (sbsail.com)