The Pailas trail will take you through the "fumerolas" and to a small waterfall (too small to swim). During your trek you will get to see, and hear, howler monkeys, white faced monkeys, iguanas, birds, butterflies, cutting leaf ants, and all sort of plants and trees.
You do not have to be particularly fit in order to complete the Pailas trail. Even families with kids can do it. The terrain is mostly flat.
In the picture you can see the waterfall.