It is very practical to make day trips from San Pedro to mainland sites/activities. Guides offer many different day trips to ruins, cave tubing, zoo, manatee, river wildlife, etc. It is usually an all day trip - you are picked up by boat 7-8AM at your hotel dock and returned 4-6PM same day. Some bus transportation (arranged by the guide) is frequently involved once your boat reaches the mainland. Your guide stays with you the entire day and meals are provided or arranged for on the mainland. The boat trip one way to the mainland is about 1 1/2 hours. Recommend you check out Tanisha and Seaduced for their offerings. If you have a site you want to visit that guides do not offer, ask one of the guides how you could make arrangements for that trip - they will have good ideas. Happy times and travels.