Rustic Falls on the road south of Mammoth Hot Springs is a nice, short stop as one heads into the park.
This lovely little roadside waterfall can be easily missed, but is worth the stop. Is it a triple plunge waterfall on Lava Creek set in a steep canyon. In the winter, Undine Falls can ice over so no flowing water is visible.
Terraced Falls is a 120 foot triple plunge waterfall in the Bechler Region of Yellowstone. The Bechler is in the southwest corner and it also called the Cascade Corner due to the high number of waterfalls there. This waterfall is accessed from the Grassy Lake/Reclamation Road by a 4 mile roundtrip hike.