Parque Nacional Rincon de la Vieja, Rincon de La Vieja

This national park must be in your top list of Costa Rica attractions to see. A true show of nature's power. The volcano loop is about 1.5h in which you observe the results of the strong Geothermal energy released by the volcano: fumaroles, ebullient mud pools and bubbling acid lakes. Can see the volcano puffing, but can't climb it, due to ongoing warnings. The longer trail (3h) goes through luscious forest and leads to majestic waterfalls where your can swim (before noon). Paths are nicely maintained. Definitely worth $16. If interested, on the road leading to the entrance there are geothermal energy conversion plants and can see giant green pipes harvesting hot water and gaseous vapours from the volcano to produce green energy. Really interesting

Be prepared to walk into primordial times when you enter this park. We went in January, and the sun was still searing. Add to that the heat from the sulfur pits! Very cool to see the earth bubbling beneath your feet and expunging hot gas into the air! We also walked under some very old trees with sloths in them, as well as saw iguanas and lizards chilling on burning rocks.