I've personally have been there myself (Way before the Ghost Tours). It's a very imposing place. Heck! All of St. Augustine is just plain creepy!
Here's a little info from wiki about the Castle:
" Ripley's oldest Odditorium, located in the Castle Warden, was purchased shortly after his death in 1949 and opened in 1950. Prior to becoming home to Ripley's vast collections from his many travels, "The Castle" as it is known, was once a hotel which played host to many famous guests, including Ripley himself and author/owner Marjorie Kinnan Rawlings. "The Castle" was originally a Moorish Revival style mansion, built in 1887 by millionaire William Warden as a winter home. The popularity and success of this museum led Ripley's associates to open new establishments throughout the United States and the world. But "The Castle" remains the permanent home of Ripley's personal collections and is the flagship of the Odditoriums. Perhaps not surprisingly, it is also rumored to be haunted. Segments of the most recent Ripley's TV series were filmed here, including the opening credits. Among the attractions here are a mummified cat, a 1/12 scale model of the original Ferris wheel made out of Erector sets, life and death masks of famous celebrities (including Abe Lincoln), and shamanistic apparati from cultures around the world. This Odditorium has always been famous for its extremely popular one armed magician, Douglas Schnittker."
It seems during the 1940's there was a fire at the Castle that killed two women. Some claim to smell smoke. Others feel the uneasy feeling of dread. Lately people have called the police because they claim to see a woman at the third floor window, screaming! The eerie thing about this is. The windows have been boarded up since the '50s.
This upcoming investigation is not being filmed for the Ghost Hunters series. It's a private investigation for fans. You can check if there's still tickets at the TAPS website.
Ripleys St. Augustine, FL