在travel all around the globe 短语中，around 是介词，around the globe 是介词短语。all是程度副词，修饰around the globe 这个介词短语。all 修饰介词短语是很常见的用法。例如：

Radio Beijing sends the news all over the world. 

北京广播电台向全世界播送新闻。

All at once she lost her temper. 

她突然发起脾气来。

Pine trees were planted all along the river. 

沿河两岸种着松树。

Their boss kept them all on their toes. 

他们的老板让他们一天到晚忙碌着。

He lives all by himself in that large house. 

他独自一人住在那所大房子里。

She is all in favor of my suggestion. 

她完全赞同我的建议。