Mr. Tumnis' Post is located on the property of the formerly famous Doneckers high end fashion store, and accompanying resturant. Doneckers started up in 1961 and drew people in from Philadelpia and many other surrounding urban areas. After some time of decline, the great recession of 2008 was the final nail in the coffin. They closed thier doors and all but left these building and parking areas to the sands of time.
Watch out, this is a high muggle zone. Take extra care for stealth. There are some locals in on the cache, but most are not. Please make note of where you are coming from in the various logs, such as city and state/country.
If you are famliar with C.S. Lewis' Narnia series, the title of this geocache is your first clue.