went to; ended up going to (often conveying completion, departure, or regret, depending on context)
→ に
phraseUncommon#15,622
went to; ended up going to (often conveying completion, departure, or regret, depending on context)に marks the destination, 行って is the te-form of 行く (to go), and しまった indicates that the action was completed; it can also convey regret or an unintended outcome.