Board Thread:Questions and Answers/@comment-26009886-20150118153540/@comment-25889587-20150118161010

There will always be one Mystery Box per game in the hidden ruins. You can enter the hidden ruins and found the mystery box in your first visit. However, if you missed it, you can keep going to the hidden ruins and you will encounter the same mystery box. Until you collect it, the mystery box will re-appear at will.