The biggest obstacle? Money, of course.
Ohio State University is trying to raise $2.5 million to finish making improvements to the majestic, four-story summer home that Abraham Lincoln's Civil War financier built in the 1800s.
Only a select group of people, including dignitaries such as Gov. Bob Taft and area congressmen, plus various journalists and others lucky enough to be part of invited tours, have been inside the mammoth structure in recent years.
Some have seen its gorgeous hardwood rotunda and its multistory bay windows where Jay Cooke, one of the 19th century's most influential bankers, had a cozy library. Others have had a chance to go up through its winding spiral staircase and through a tight portal leading to the observatory.
Countless visitors strolling the boardwalk of Put-in-Bay have been intrigued by a lakefront view of the stone, Italian-styled castle and its gothic tower that rises above Gibraltar Island's trees.
Some $1 million has been raised and spent since 1996 to renovate the historic building's exterior, including $500,000 from the Ohio General Assembly to stabilize joints and do other work.
About $2.5 million more is needed to renovate the interior, said Dr. Jeff Reutter, director of OSU's nearby Stone Laboratory and one of the project coordinators.
Registered as a federal historic landmark in 1966, the mysterious castle is not open to the general public and likely won't ever be, Mr. Reutter said.
It is on a quiet, six-acre island practically a stone's throw from the souvenir shops and taverns of touristy Put-in-Bay.
Gibraltar Island was donated to Ohio State by industrialist Julius Stone shortly after he had purchased it in 1925 from Mr. Cooke's daughter, Laura Cooke Barney.
Mr. Stone, a former OSU board of trustees chairman, donated it to the university on the condition that the nearby research station, which was called Lake Laboratory at the time, be renamed after his father, Franz Stone.
Ohio State envisions Cooke's Castle as a conference center and library for Stone Lab, America's oldest biological field station.
After all these years, Stone Lab is still one of only two Great Lakes research facilities that exist on a Great Lakes island. The other is Central Michigan University's laboratory on Beaver Island in northern Lake Michigan.
Cooke's Castle was last used in the early 1980s, when it was a men's dormitory.
Mr. Cooke, a Sandusky native, moved to Philadelphia and became affiliated with Mr. Lincoln's secretary of the treasury, Salmon Chase. From that association, Mr. Cooke helped Mr. Lincoln finance the North's victory in the Civil War by selling a then-incredible $950 million of war bonds.
An avid bass fisherman, Mr. Cooke bought Gibraltar Island in 1864 for what would be a bargain in today's dollars, a mere $3,001. He built the castle there a year later. He and his family spent four to six weeks a year on Gibraltar until his death in 1905.