It is 1 1/2 hour each way. While the rain forest is worth the time to get there, I think the BEST way to see the rain forest is via private car. You can stop and explore along the way, wander some of the paths on foot, etc. It is not nearly as interesting from a tour bus. If it were me, and I really wanted to see the rainforest - I would rent a car for the day. However, if you don't wish to venture to the other side of the island AND this is your first visit to San Juan, there is a lot to see in Old San Juan and the surrounding areas.