This almost-matched pair of townhouse apartment buildings at 316-318 East 77th Street on the Upper East Side is fronted by nondescript, fairly utilitarian facades, but the rear courtyard “rocks” an historic secret in the form of a massive chunk of Manhattan bedrock known as Lion’s Rock. In recent times the property was the site of a restaurant by the same name. The big boulder was part of the establishment’s rear garden, complete with water trickling from a spring that was a part of the old Saw Mill Creek. Lion’s Rock restaurant closed in the 1990s, but the rock remains (and probably will for the foreseeable future). But more interestingly, the rock is all that remains of a very different Manhattan.