For the purpose of developing a proper and suitable entrance road to the Mammoth Cave National Park, the Secretary of the Interior is authorized in his discretion to accept on behalf of the United States donations of lands, buildings, structures, and other property or interests therein, or to acquire such property with donated funds by purchase, condemnation, or otherwise, within an area or areas to be determined by him, but (a) not to exceed one mile in width, extending from the exterior boundary of the Mammoth Cave National