Here's the answer:
“よい旅を”
(yoi tabi o)
Watch a real native speaker say it:
Here's how it sounds in a textbook:
Fun fact: the hundreds of thousands of people learning Japanese with Memrise get this phrase correct 89.92% of the time!
(yoi tabi o)
Fun fact: the hundreds of thousands of people learning Japanese with Memrise get this phrase correct 89.92% of the time!