Replying to Travel around Central America

In May I'll be attending my school's group study program in Belize. While there I'll be working in everyday in the jungle with the howler monkeys and living next to the beach in Placencia. I've booked my flight out of Managua 3 weeks after the program ends and will be traveling with a group of 2 - 6 other girls. Our plan currently is to head straight into Honduras to take an intro scuba course at Utila then make our way down to Nicaragua.

To any of you who have traveled around Central America, I'm looking for recommendations on absolute must-sees in Honduras/Nicaragua/maybe El Salvador and Costa Rica. We're all pretty active/not afraid of dirt but we will have spent the last 3 weeks working pretty hard so we'll probably want to keep things low key. Good surfing, cool hikes, fun towns are perfect. Things need to be kept as cheap as possible because we're all broke college students so stuff like ziplining is out of the question. If you have any other travel advice I'm happy to listen to it.