I had NEVER seen so much greenery in my life... If you're planning to go ziplining in Costa Rica, I highly recommend having the experience in Arenal. The air is so fresh and pure, the plants and trees are so full and healthy and the view is mesmerizing. Tip: Rumor has it you can see both Arenal Volcano and Lake Arenal in entirety on a clear, sunny day.
Arenal Volcano National Park offers more adventure options than any other place I've been. If you like to feel that pit in your stomach when you're about to embark on an activity that slightly scares you then come to Arenal! This photo is from rappelling down a waterfall along the Sky Walk trail, but you can also walk along suspension bridges and zip-line at 50+ miles an hour above its rainforest in the same area. Pretty awesome.