"I think it'll have an airy, porch-like feeling," Didden said.
Carved into the ground behind the library about 15 feet below street level would be about an additional 2,700 square feet of space for a children's library.
Natural light would come into the underground space from the skylight above. The center of the new room would be left open for public meetings while children's books and activity areas would surround the sides.
"I think it's unrealistic," said Rusty Berry, a Shepherdstown businessman who opposes the library's plans.
"The library definitely needs to expand. There's a lot of talented and hard-working people at the library. I just don't think they've looked at all of the other options," Berry said.
Didden said she's heard all the criticisms from various people - from complaints about the $500,000 estimated cost of the project to concerns that the changes wouldn't fit the building aesthetically.
Didden said the library board has worked on the plans with an architect for three years.
She said the U.S. Department of Interior guidelines were followed - though that was not required - on how to make proper additions to historic buildings. The federal guidelines suggest not to attempt to match the current architecture but to build an addition that does not detract from the existing building, she said.
No changes would be visible from the front and sides of the building, she said.
The cost may seem high, but she said she believes it is a good investment in the future.
The addition would make the library safer by adding fire exits and making it accessible to the disabled, Didden said.
The children's library would be moved from the current site on the second floor to the new addition, allowing for more books on the second floor.
The library has about 16,000 volumes squeezed into its current space, including shelves in the kitchen area.
Building a new library would mean placing it outside Shepherdstown, where land is expensive, Didden said.
The library board wants to keep the library in the center of Shepherdstown, she said.
Didden said she believes there are a lot of misconceptions about what the back addition would look like.
She said that based on an artist's drawing of the addition, people believe it would be all glass. From street level, people would see the knee-high brick wall surrounding the addition and there also would be brick columns, she said.
Didden said the library board will attempt to get approval from the Town Council on Tuesday to extend the library's lease and to get permission to use additional space for the expansion.
Didden said she was surprised by the public opposition during the first public meeting about the library's plans on Dec. 18 .
Since that meeting, written comments are running about 3-to-1 in favor of the library's plans, said Shepherdstown Mayor Vincent Parmesano.
Parmesano said he is neutral about the library's plans, but believes more room is needed for the library.
"They're running out of space," Parmesano said.