travel in 在哪里旅行 （也可以理解成一个可以延续的状态）；
travel to 去那里旅行 （也可以理解成一个一时的动作）。
You\'ll have to travel in disguise
你只能乔装出行。
They travel in convoy with armed guards.
他们的`车队在武装警卫的护送下行进。
Many people travel to work by car
很多人开车去上班。
He was too sick to travel to his son\'s side.
他病得厉害，不能赶到他儿子身边了。
