To find the Bonus Cache, solve "A Stroll Through Old Jaffa" - Adventure Lab.
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The tour takes you through the old city of Jaffa, showing you some places that are common and some that maybe you won't see when visiting the city normally.
To find where this cache is hidden write down the values of the letters you find while solving the lab-cache.
The final location will be at:
N 32° 3.{A+B+C} E 34° 45.{C+D+E}