This diamond mine is perhaps one of the easiest of RollerCoaster Tycoon 2's Challenging scenarios. Players have two years to accumulate 900 guests.
A solid start would imply placing a food stall, a Drinks Stall, an Information Kiosk, a T-Shirt Stall, and a Restroom at every corner in the pathways. Then, players can choose to edit the Wooden Roller Coaster (by adding more trains and perhaps deleting the entrance at the bottom), and connect the pathway to other pathways. A mechanic set to patrol at the top portion of the Wooden Roller Coaster, and another at the bottom, will prove a lifesaver at this point.
The diamond mine, due to its configuration, is a pain to keep clean - there is a huge amount of pathway, and the trash will be scattered with no focal points, so players will have to hire a lot of handymen as soon as it is required to clean it up. First Aid Rooms are also a valuable asset near the exits of nauseating rides.
After the park starts picking up steam, players can freely charge $20 to $30 for the entrance fee. Clearing all the scenery in the bottom of the park can net a helpful thousands of dollars, which could get players enough money for a Corkscrew Roller Coaster.
Basically, once all of this is done, the guests should accumulate themselves without barely any effort. In fact, it is possible for players to get 900 guests by the end of Year 1. Just a new ride or two every once in a while will help reaching the goal, as long as there isn't any litter or vomit.