When the National Underground Railroad Freedom Center opens in Cincinnati in August, it will join a number of institutions already battling for tourists' dollars. The center's supporters are raising the last of the 110 million dollars needed to build the riverfront museum. Once it opens, it will need to raise at least ten million dollars a year to keep operating. That money will come from ticket sales, private and government grants and gift shop profits. Other museums such as the Rock and Roll Hall of Fame in Cleveland and the Cincinnati Museum Center have struggled in recent years because of a drop in tourism. Museum and tourism experts say the Freedom Center will need to do several things to succeed, including attracting visitors from around the country, securing corporate sponsorships and establishing an endowment.