Mega Park is the reward for completing every original RollerCoaster Tycoon scenario. Every ride, shop/stall, and scenery item is available through research in this scenario. The park features theming from many other scenarios in the original game. There is no objective for this park, but it uses money, which means it isn't a true sandbox mode. However it's definitely worth working hard to unlock.
Since there is no proper objective, no guide's truly needed. Mega Park can almost be thought of as a sandbox ; the only thing stopping it from being an actual sandbox is that players still start out with $10,000 and a $50,000 loan, due to the fact that scenarios could not have unlimited money in the original RollerCoaster Tycoon. Still, players should take the objective the developers give them to heart : having fun !
Several sections of the park appear to have welcome some kind of previous landscaping. There are channels dug into hillsides, as well as fences indicating a possible path for tracked rides.
The Megaworld Park scenario in the Loopy Landscapes expansion pack is a developed version of this park which does not use money. However, there is an objective in it, so it is still not a true sandbox.
Comparing the landscaping done to the Mega Park to the locations of the coasters in Megaworld Park, it's noticeable that this park was planned ahead while RCT was in production.
Some areas on Mega Park are exact copies of the landscapes of the original Roller Coaster Tycoon scenarios :
The others are hard to notice due to the fact that they are turned into hills.
In Roller Coaster Tycoon Deluxe, the scenario will appear on the Extra section, and not below the list of the original RCT scenarios like in the original game. It is succeeded by Whispering Cliffs, the first of Added Attractions scenario tab.