The cache is located at the Needle's Eye, one of the 4 monuments/follies on the Wentworth Estate. The Needles Eye was built sometime in the 16th century, but the exact details as to its purpose and meaning are obscure as no records remain.
Many interesting theories and myths surround it from driving horse and carriage through it as a test for coach men to the Fitzwilliam’s, to a shelter for pall bearers carrying the deceased from the Wentworth estate to nearby villages. You may also like to search for the alleged musket ball impact marks on the south eastern face, touted as evidence of an illegal execution during the civil/Jacobean war
More reading/background as to its design and purpose of the Needles Eye are available at http://www.wentworthvillage.net/ and is well worth visiting before your expedition to this and the other Wentworth Wander caches to make your day more interesting and worthwhile.