"When I was a kid, I could NOT wait for any field trip!"
After the field trip you can incorporate the place that you went to in your lessons and keep the students interested. Instead of just giving the students a word problem like they see every day, write one that incorporates your field trip. Even have the students write problems for each other to work out that involve the field trip. The more you do to make the learning a real world situation, the more the students are going to retain.
The more excited you get about the learning, the more excited the students will be!