Preservation-minded buyers will be delighted by the 4,700-square-foot Federal-style house at 404 West 20th Street; the Chelsea Historic District designation identifies it as the oldest house in the district, dating to 1830. Clement Clarke Moore owned the land, and a man named Hugh Walker leased this parcel for just $40 per year to build this house, which has a wood frame and brick front. The original clapboard siding is still visible on the east side of the house, but the facade, front door, and cornice were remodeled before the landmark designation in 1970. Inside, the house is currently configured as three units, and needs an "architect's creative vision" to revive it, but a lot of historic details remain, including two original Belgian marble mantels, carved moldings and a staircase, and wide-plank hardwood floors. It's asking $6.5 million.