The Cow Level lives in HotS

Blizzard has, for years, been denying allegations of hiding secret "cow levels" in their games, especially the original Diablo, where the rumors first began. (If you clicked a mysteriously-spawned cow several times, it opened a portal that led to a secret area, hence the name.) Descriptions vary from report to report of what exactly a "cow level" is, but they are generally accepted to be secret areas that contain significant numbers of bovines (sometimes including powerful, magic-wielding bovines) and little else. So prevalent were claims by fans to have found the "secret cow level" in any number of Blizzard's games that their repeated, pithy response became a common utterance for fans: There is no cow level.