The phrase "lit upon" is often used to describe accidentally discovering something or stumbling upon an idea. However, there are several synonyms that can be used in its place. For example, "stumbled upon" or "chanced upon" can be used to describe a random encounter. "Came across" or "found" can be used in a broader sense to describe discovering something new. "Unearthed" or "discovered" can be used to describe a significant and meaningful discovery. Ultimately, the choice of synonym will depend on the context and tone of the sentence, but these alternatives provide flexibility in describing unexpected discoveries.