The listing claims this house at 351 Riverside Drive is the only freestanding single-family mansion remaining in Manhattan. True? We do know that it's had a tough few years on the market: it was asking $31 million in 2006, $30 million in 2007, and $25 million last year. It's now up for sale again for the slightly tweaked $24.9 million. The 41' wide house (with 12,000 square feet of interior space) was built in 1909 by Carnegie Hall designer William Tuthill, and current owner Hans Smit has been restoring it ever since picking it up from Columbia University for $325,000 in 1979. Smit doesn't live there, but it's been the location for film shoots (including Woody Allen's Bullets Over Broadway) and the pizza parties Smit holds for his law students. Nothin' like eating a slice in style!