It was a Japanese or Japanese-based animated film from around 2010-ish, maybe earlier. I can't remember if there was any talking in it (might have been a silent). It follows a girl who is either living at or visiting a relative (maybe a grandma) and finds a portal to a spirit realm via a well or pond. Upon entering, she finds a world full of anthropomorphized animals, in particular a rabbit that gives her a mask to disguise herself from evil spirits that inhabit the land (humans are not allowed). There is a train in there, I think, or some other method of transportation that keeps the girl safe from the spirits. In the end, the girl is detected by the spirits, and is forced to escape back to the human realm. The rabbit in the end, if I remember correctly, destroys the portal in the end, forever sealing off the two different realms.
Sorry for the rough and possibly inaccurate description, but I hope this is enough. Thank you.