The northernmost of Central Park West's storied towered buildings, the El Dorado boasts some seriously baronial apartments, but for something truly outsized, the sellers of units 3E and 3F are joining forces to propose a six-bedroom, 6.5-bath, 4,500-square-foot combination. Listed for $8.9M, the two units have yet to be combined—a task that would surely require many millions more—but plans have been drawn up to give potential buyers some idea of the possibilities. The projected floor plan calls for an expanded kitchen, opens up space for a wine room, and adds a laundry. In an odd twist, the plan also includes walling off an existing bathtub. Wall safe? Panic room? A purist desire for a true powder room? Either way this combination is an innovative solution for the owners, who are going up against eight other on-the-market apartments in the building.