eye-opener
noun/ˈaɪ əʊpənə(r)/
/ˈaɪ əʊəpənər/
[usually singular]- an event, experience, etc. that is surprising and shows you something that you did not already know
使人大开眼界的事情（或经历等） - Travelling around India was a real eye-opener for me.
周游印度真让我开了眼界。
- Travelling around India was a real eye-opener for me.