Be sure to check out the History of the Des Moines Renaissance Faire to see the evolution of the event.
Festival Park is located just behind Sleepy Hollow Sports Park near the Iowa State Fairground.
See panoramic (VR) views of the site just as construction was beginning.
And here is what it looked like from above before construction:
Here is an architectural rendering of Festival Park (from 2005):
And here's a sketch of how it actually turned out (from 2009):
Parking and event entrance is at the top left of the map, across the river. The "main street" area leads southeast to the banquet hall building. A performance field is behind it, to be used for renaissance festival jousts, wild west shows, and other equestrian demonstrations. At the top right is the castle building which serves as backstage area for event staff (dressing rooms, shower facilities, offices, storage, workshop). The forest area on the left is the fantasy realm and pirate's cove area.