One of Dallas’s best-kept secrets remains just as recondite as it was during its Prohibition heyday. Top o’ Hill Terrace, known to some as “Vegas before Vegas,” was designed and built to cover outright debauchery under a façade of only the most prim and proper dining that the suburbs of Dallas could offer. Top o’ Hill Terrace began its life as exactly what it seemed to be: an exclusive, upstanding restaurant nestled in a beautiful, spacious campus at one of the highest points in the county. But with the opening of…