The Mount Vernon carriage house, constructed in 1799, is one of those rare city gems that endures in spite of the rising buildings around it. Especially for City kids, Mount Vernon possesses a historic authenticity that only a few places in New York can claim. This Friday, the museum is opening its doors to welcome families for a candlelit museum tour and spooky storytelling by Gerald Fierst, the 2003 featured ghost storyteller at the International Storytelling Center.