There are usually multiple strategies to successfully completing a scenario; these can be discussed on the scenario's discussion page or written down in an existing or additional section of this article.
One of the first things to do when facing Fun Fortress, is to remove the walkways on the walls and inside the castle, as it will both prevent guests from getting lost and return about $4,000 to the player. After that, time to build some rides : A gentle flat ride near the entrance, a small roller coaster like a Wooden Crazy Rodent Roller Coaster, and some more gentle and thrill rides inside the small, enclosed area. After that, the park will need some stalls. As plenty of roller coasters are available from the start, researching roller coasters will be useless in the beginning.
The main difficulty here is the terrain. Lots of hills that force the player to plan paths and rides accordingly, a good strategy is circling the hills in the middle by flat rides, and in the end, making a coaster (probably a Vertical Drop) above all of them.
The guests in this scenario are quite rich ($65 - $95) however, which allows to player to charge more at the game than in previous scenarios. A good start would be $30, with a gradual increase over time up to $50 or even $55. A handful of exciting roller coasters will be needed here to attract the required amount of guests, especially in RCT1 : Block brakes allow for more guests per coaster in RCT2, which will ease the process. In both games, marketing can get the few missing guests as the deadline comes.