21 East 61st Street #15A Upper East Side, New York New York 10065

LLNYC's look at listings:

Thanks to a wealth of differing definitions, we’re still not entirely sure what constitutes a cond-op, but this 4,649-square-foot Carlton House pad apparently is one, according to StreetEasy.

The spread, which is now seeking $21.5 million, has been on and off the market since 2013, with its asking price starting at $21 million. It's the most expensive unit at the building right now but its upstairs neighbor is also up for grabs, but at a slightly cheaper $19.9 million -- perfect for anyone who dreams of duplexes.

The four-bedroom home comes with a marble entrance foyer, casement windows, Central Park views, a library, a formal dining room, and a private bedroom wing.

Carlton House was originally designed in 1940 by Kenneth B. Norton, but construction was stalled during World War II. It was eventually completed in 1950. Now, in classic New York style, Extell Development is turning the spread - that was once a hotel - into luxury apartments.

Amenities include a fitness center, an indoor swimming pool, steam rooms, a game room, and storage.

Michele Kleier, Sabrina Kleier-Morgenstern and Samantha Kleier Forbes of Kleier Residential have the listing.

Unit Details:
Property TypeOther
Size 4,649 ft²
Price Per ft² $4,624
Maintenance $14,762