This hole in the ground is the length of three city blocks. It is a carpet of sand, weeds and prairie grass sloping down to the river, interrupted only by a low ridge of broken bedrock. Around it, a black chain-link fence catches the plastic cups, paper and other debris that roll along like tumbleweeds.

But this 6.4-acre parcel is not sitting in the middle of a decaying rust-belt city. It is nestled in the middle of Manhattan, between 38th and 41st Streets on First Avenue, overlooking the East River, amid a residential real estate boom.

Yet it has sat fallow for six years, long enough for young trees to rise at the edges of the property.

How one of the most valuable undeveloped pieces of earth has sat empty for years — even after New York City approved a $4 billion project there in 2008 — is a mysterious and confusing tale of ambition, infighting, clashing personalities and bad timing. At its heart is Sheldon H. Solow, an irascible but talented billionaire developer who is an intermittent presence in his office on 57th Street after a career that reaches back more than a half century.