This is where our regular practice fields are. Here's a nice map to help you find it. Your goal should be to get onto 55th St, which is the north border of the campus (Pierce Tower and Ratner are both on 55th and it is a busy four-lane street). Then travel west; you will simply arrive at a grassy open area. Look for flying discs.
Eckhart and Bartlett Quads, North Field, Henry Crown, Ratner, etc.
The map site provided above can help you out. Starting on the main quads, go east on 58th Street and pass the Graduate School of Business (large modern-looking building). You'll see the lab schools on your right, beginning with Judd Hall, then the fenced courtyard and central buildings. Turn right at your next available opportunity, which will take you between the main buildings on your right and the gyms on the left.
The Pepperland
This is a cluster of apartments largely inhabited by Ultimate players, and as such it is a home base for Junk. It's a fun place to be. To get there, get on 57th Street. This is the street running west to east featuring landmarks such as the Reg and the Reynolds Club. Now start traveling east away from campus. You will pass the Quadrangle Club on your right, along with 57th St. Books, the Med, and Noodles, Etc. You will pass Salonica on your left, and when you reach Harper Ave (this is the intersection right before Powell's Books) turn right and walk on the left side of the street. On the next available sidewalk, just a few yards down the street, turn left and stop at the first door. You've reached the Pepperland.
To recap: go east on 57th until you reach Harper Ave, then turn south (right) and walk several yards until you turn east (left) at your first opportunity on the east (left) side of the street.