。
Nothing is as fun as traveling.
Literal
Travel [extent-ほど] fun thing [topic-は] doesn't-exist.
~ほど~ものはない is the 'nothing is as X as Y' superlative pattern, here used to praise travel as the most enjoyable activity. The polite ありません lifts the register slightly above plain ない, making this fit for a polite conversational compliment.