Park Slope townhouses are in such high demand right now that it seems like there's a new one going into contract every other day. Today's is 620 3rd Street, a four-story brick two-family, which was listed in November for $3.35 million. No word yet on the final sale price, but if the other $3+ million Park Slope townhouses that entered contract in the last couple months are any indication, it probably got close to its ask, if not more. Still on the market in the Slope: 861 Carroll Street (asking $4.198 million), 592 3rd Street ($2.85 million), and, of course, the Tracy Mansion, which had its price slashed by $7 million last month. That last one might be a slightly tougher sell.