you should definitely do a waterfall with various levels of plants and moss and try to make an ecosystem out of it. pic a region of the world that interests you and one that you could have access to its native plants, then research small reptiles or amphibians that interest you from the area. for example, the northwest has some nice species of moss. You could also add some of the newts and salamanders from that area. a multi-tiered waterfall would look amazing!