From "South" to Purdue Union Club Hotel:

Take I65-North, exit to St. Rd. 26-west;

drive a few miles on Rd. 26, across the Wabash river, go up the hill to Purdue University;

turn right onto Grant Street get in the left lane quickly because the Purdue Memorial Union is the first building on the left.

From "North" to Purdue Union Club Hotel:

Take I65-South, exit to St. Rd. 43-South;

drive a few miles on Rd. 43 (which is also called River Road) and turn right at State Road 26 (also called "State Street");

go up the hill and turn right onto Grant Street (which is a one-way street) and get in the left lane quickly because the Purdue Memorial Union is the first building on the left.

Parking at Purdue Union Club Hotel:

When you arrive, you can park temporarily in the entrance drive to the Union Hotel while you check in. They will give you a parking voucher at the front desk and you can move your car across the street to the Grant Street parking garage.

From the Union Club Hotel to the Math Dept:

Ask for a map at the front desk of the Union Hotel. Go out the front door of the Union Hotel on Grant Street and turn left. Walk up Grant Street and turn left on the first big sidewalk at the corner of the Union. You can now see the Math Building looming in the distance (200 yards away). The Math Building is a large, light red brick, plain looking, rectangular building which is the tallest building on campus. Take an elevator (on the left side of the building only !) to the 8-th floor.

If you drive and do not stay in the Union Club Hotel:

Go to Purdue Parking Facilities at 1404 W. State Street on the West end of campus, and buy a one-day parking permit.

Park your car in the University Street Parking garage. To get to the parking garage from the Parking Facilities office go back East on State Street, turn left on University Street; the parking garage will be on the left side after 2 blocks.

Go out of the parking garage, walk across the Northwest Ave, the MATH building (a rectangular 9 story building) is just a few blocks ahead;

take an elevator (on the left side of the math building) to the 8-th floor.

Maps and more information can be found at here.