Being in the same classroom all day, every day can dampen kids' spirits. A field trip is a chance to do something new and different in a new environment, breaking away from the humdrum school routine. This can reinvigorate children and breathe life into lesson plans.
A field trip to a museum gallery or exhibit can not only give students something new to see but also reinforce concepts learned in the classroom. Learning about a scientific process, for instance, which is then illustrated in a display at a science museum, offers students a chance to see the science, which they have already had explained to them, in action. A field trip can also present students with a lot of information tied together neatly, making it easier for a teacher to explain a certain concept, situation or historical period.
Seeing a historical artifact in the classroom is one thing, but it may be difficult for children to imagine that same artifact in the historical context from which it came. But actually being at the excavation site where the artifact was found allows a child to engage with the history he is learning and gain an insight into the bigger picture. Although this example is historical, field trips are useful for allowing this engagement within any subject.
Though we can use technology such as video and the Internet to offer kids glimpses, it can be difficult to get across the true spectacle or meaning of something without taking the class there. An impressive building, for example, doesn't look half as awe-inspiring when viewed on Google image search as it does in real life, and it may be hard for kids to truly understand a subject from the classroom.
Field trips provide an opportunity for students to learn key skills which are tough to impart in a school environment. For example, the ability to comprehend from what is around you is difficult to teach without the student actually being in a situation where she must use that skill.